okay if this thing goes off let me know it's gone off twice I don't know why what's the last thing we studied what well that sucks yeah I don't know it just keep on having to select the source doc you got a phone what the number eight you got it eight four five oh eight oh seven as long as I keep selecting the source I don't know why it drops the source makes no sense ask it tell them it's in room 118 if they got a chance they welcome just come on in the class see if they can figure out why it's I got to keep hitting doc cam because it goes off civil engineering 118 I'll be done yeah but I got a student worker in here I'll get him if you push a button this is really strange but better than not having class I'm gonna grab a chair if you want to yeah when it goes off you just select source document camera and it turns back on okay I don't get it okay no no no go right here all right we were talking about columns sorry for the delay columns fail by having so much load on them that they buckle we have equations for the loads that it takes to buckle them we have mr. Euler's opinion which is accurate up to some breakpoint from which we find some of the fibers will go into the plastic region and of course when they all go to f sub y his opinions aren't valid mainly because the fibers are no longer in the straight line portion of the stress strain diagram e well the same problem happens locally but we've done so far as what they call global buckling for the whole column buckles but a second possibility is that these little stick out pieces here when you put a uniform stress across them there's so much stress that they will personally buckle if they're too thin so you have to check for local buckling as well as global buckling the phenomena is very similar up to some point these things won't buckle they're just too short and they're too squatty for instance if you make me a wide flange that looks like that then this piece just not gonna buckle locally it's too thick and doesn't stick out far enough now if that happens the real reason the whole column fails is not that it's buckled it may still be straight come on in yeah and they'll probably figure we just have to keep on pushing the button that says what a dock cam and it comes right back up and you have to sit here how long a minute two minutes okay this is my entourage incidentally we travel together there's two types of these things one of these elements like an element of a flange is called an unstiffened element means it is supported only on one edge a stiffened element is one that's harder to buckle because it is attached at two edges so they'll have different numbers whether or not it's a unstiffened or a stiffened element your personal column will be classified as either a slender or a non slender column if these little stick-out pieces have a tendency to buckle then you have got what we call a non slender column the limit state will be caused when the local piece locally buckles and the equations you've been using up to now won't apply now here's kind of what they look like in at some breakpoint on these flanges and webs they'll tell you what that break point is it depends on what it is and what it's attached to if you are to the left of that point you don't have to fiddle with it your equations that we worked out so far work perfectly on the other hand if you exceed this breakpoint then you will have to reduce the load you will get local buckling there is a symbol that they use just generic and it's lambda and that lamb does just something we've got to call the thing something so I'll say are you above or below the breakpoint are you above or below the lambda value for your wide flange or for your channel or whatever you're working with they give that the name lambda your personal value for your personal wide flange is just going to be listed as lambda if you're want to know where the break point is it's subscripted with an R like the radius of gyration of the little piece that's sticking out is so small but that's the that's the breakpoint if you remember previously we had a curve looked very much like this one for the column strength that came in at f sub y and it had a breakpoint above which mr. Euler's equation with a point eight seven seven attached to take care of things like how straight the columns are when you buy them and an equation to the left we have the same kind of a deal you're going to have a breakpoint your lambda the way you calculate lambda will be how far does the little piece stick out divided by how thick it is and how far it sticks out and how thick it is is dependent on are you talking about a channel are you talking about an angle are you talking about a wide flange but there'll be a b over t ratio for a wide flange or a t this is what you and I have been calling b sub f so far it sticks out in two directions how far the flange sticks out is b sub f over two b sub f is out of the book and then your t will be the t of the flange and that's a measure of its susceptibility to local buckling so you go get your wide flange and you calculate b sub f over two divided by its flange thickness and that'll be your value your value is to be compared with the number that we have found below which don't care above which you have problems this number just like the number we found before if you remember Mr. Euler came in and was doing great right about this point he wasn't doing so great we had a break point above that break point you used Euler's equation for the critical buckling stress f sub e put times point eight seven seven then you had a different equation something raised to the power raised to the something times f sub y below this break point we got break points in this kind of work all over the place the break point for a wide flange is point five six times square root of e over f sub y and that may be the number for something else we just have to see but it costs a lot of money and they can tell you that this is what it's a factor a function of it's all steel so this will always be 29,000 if you have a wide flange made out of 50 ksi yield steel then that's just a number you crunch that number out turns out to be 113 if you have a wide flange made out of a 36 steel I'm not sure you know why you would do that because it's not gonna be as strong you don't have to be a lot more steel involved but you take e over 36 ksi time square root time point five six and that would be the break point above which you have problems with the local buckling below which you do not here's another thing that can buckle this is the flange of a wide flange it's also the flange of a tea because teas are cut from wide flanges here is the web of a wide flange and the supported length is right down here a little bit below where this radius comes out and right above right there where that radius comes out and the tendency to buckle is what they call H you can get H by measuring the depth of the wide flange you subtract a thing called K there are two of them in the book one of them is K sub DES for design and one of them is K for sub DET for detailing detailing as you might imagine they tell you that number usually in sixteenths of an inch so you can tell whether or not you can get a wrench in there and tighten up bolts and stuff like that you want the design number it's not hard to tell the difference because one of them is I don't know point 106 and one of them will be plus the flange and one of them is a sixteenth number we don't use anything that are sixteenths those sixteenths are used to see whether or not you can fit things together depending on how long this is if it's very long you see how it has a very high lambda and if it is very thick it'll have a lower lambda telling you whether or not has a high susceptibility or a low susceptibility the break point for the web yeah break point for the web is one point four nine this is the break point for the flange now I don't care for it but everybody says it but me they call that the upper limit and what they're really saying is the upper limit below which you're okay with the upper limit where you're getting ready to not be okay I really like to think of them a lot more like their break points between bad and good and it's going to even be more important I think when you start getting more than one break point down here because it won't be too long before we're going to have some things that go like this go like this and go like this you're gonna have a break point you can have break points so I think rather than trying to remember which region you're in figure the break point and then go get your number whatever it is for and see which region you're in there your break points base 16.1-16 table be 4.1 a here's what we said there's that number we just discussed point 56 that is for flanges of rolled eye-shaped sections did you guys fix it okay well I got my backup are these are those your keys oh okay thank you I don't get that that happened how many times five six okay flanges here are your flanges there's your b over t your b stick out is b sub f over 2 that's where you get your b over t is your measurement your b sub f over 2 of course is b and thickness here are for webs of doubly symmetric eye-shaped sections and channels that include an s shape or wide flange here is your break point on that one one point four nine here's a break point on an angle b over t here the break point on crosses here the break point on rectangular tubes here's the break point on a tube a tube as a tendency to locally buckle also your measurement your criteria for what do you have in the shape you're requesting is it's outside diameter divided by the thickness and this is no square root on this one there's a break point below which you're good above which you'll have to include the effect of local buckling yes sir it's on page sixteen point one dash sixteen sure typical there's somebody who wrinkled up the flange that is local buckling of the flange here's one that's more flange here's one local buckling of the web now in truth you'll notice rather than actually go buckle something in the flange only and then buckle something else in the web only they just went and took something made a little short column out of it and squashed it so hard everything in sight buckled but basically you see what's happening this is the problem you can tell it's not real also because generally speaking if you put too much compression across here one side will tend to go up while the other side will tend to go down in other words the whole thing will roll when it is but local buckling like this this one is pretty is typical of what you really would see if web itself buckled they wanted to get two and one on that demonstration here are typical values this is in the front of your book page 1 dash 24 for a 14 by 132 cross sectional area depth you would need the depth you would need to subtract 2 times k design it's not quite true because anything for convenience these people are going to give you they're going to give you depth minus k design over to and they're going to divide it by the thickness of the web somewhere where's the thickness there's the thickness of the web but you know you could be asked to check it on an exam check the number there's probably one or two wrong in the book and say go see what the h over t sub w is or h over to b sub f over t sub w whatever and pull the numbers out and the number in the book could be wrong but there's your depth there's your k design this minus two of these for the web divided by the thickness of the web here's your b sub f right there divided by two to get the stick out of the wide flange on one side only divided by the thickness of the web that number there is going to give you a measure of susceptibility to local buckling but in truth on the next page here they are for that same shape there's b sub f over two divided by the thickness of the flange for this shape that's your number this will have to be compared to a breakpoint here is the susceptibility to the web buckling says little h little h is actually d minus 2k designs is right there d minus 2k designs here the numbers calculated out 17.7 here's sugui's take I just put the whole table in there the same numbers there is your breakpoint for the flange there's your breakpoint for the web here's for t this is for the t sticking out the same as this one doesn't have to be it is here for the web 1.49 versus 0.75 now they don't make any sense why is d over t 0.75 and this is h over t sub w what do you think the difference is between a wide flange and a and a t they're both made from the same thing well this is a stiffened element somebody's holding both ends of it down and this is a non stiffened element this one is more subject to buckling local buckling I don't know here's two angles pair angles they're exactly the same except they got different numbers wonder why that is the gap that's exactly right these two have to be bolted together and then this part here will support each other and they make a pretty stiff little element so these things aren't as likely to fail then these here where they are they're going to be still bolted together but they probably have a washer in there like that and that washer may only occur every you know five feet or something like that these are more susceptible to buckling so you see here you have a lower number and the lower number means that further down to the left you're going to be more susceptible to buckling if you exceed that number you'll have to take local buckling into account an example I like that that's a nice ringtone man it's better than some I've heard I hate my dad and I hate my mom and I killed the cat and a blender bomb and a geez man don't go to an interview with that on your cell phone wow for a w-14 by 74 he would like you to investigate local stability this is lambda you this is the lambda of the flange this is the criteria that you were told that you must follow when you look at the table for wide flanges b over t where b is the stick out is b flange over two and then t is the thickness there's b sub f over two thickness of the flange you can check these numbers out there on these pages and you get six point 41 out of the book and this says you get 6.43 numbers change every now and then every now and then all of a sudden a wide flange will have this much cross section area and the next book they come out it's got a little bit different those things happen not exactly sure why it could I guess really be that they go out and buy a bunch of them and this major made by different people and they have slight differences and so they say okay well this year it's this number I mean you don't care not gonna change anything but if you get something like that's a little off shouldn't bother you you still know what you're doing it's just to change the numbers the break point for case one for the flange is point five six square review over f sub y there's e there's f sub y he says investigate the column of example four two that must have been a 50 ksi steel thirteen point five you are to the left of the break point otherwise if you were to plot this look something like this and here was your break point thirteen point five you are at six point four one then this is you therefore it is not subject to local buckling for this shape as far as the flange is concerned here's the web lambda for you is the lambda of the web as opposed to the flange here it's calculated you could have looked it up in the book is twenty five point four break point it's subscripted instead of by you as when the radius of gyration pretty well gives this thing problems lambda subar there's your break point number and it turns out to be thirty five point four again you are to the left of this number and since you're to the left it is not subject to local buckling so local instability is not a problem now here he tells you how to correct it if you have local buckling of these elements you have to even in this class know how to tell if it's subjected if it is subject to local buckling because what we're going to do is if we find it we're probably going to avoid that shape because we don't really have time to cover everything in the book than this is one of them we don't it's not straightforward they will do it if you go to graduate school we just don't do it in here so if you come up and you find that one of these shapes has is non slender in other words has elements which are subjected possibly not possibly but they will be subjected to local buckling then we're going to avoid them we don't have to avoid all of them because one of the things we use in here is we use tables and they'll tell us how strong something is for various shapes in the table well the guy who did the table he went to graduate school he knows how to do this and so local buckling is included in the table numbers the only thing is it's not included is if I pick a shape and ask you how strong it is and you get up to the point where you say this thing is gonna locally buckle that's gonna be the limit at that point you're gonna have to say I don't know yet that takes care of that's one of the reason we don't have time five pages ten pages of calculations and derivations good stuff as soon as they make this a four-hour class we'll cover that quick review this is global buckling and the reason I know it's global buckling is because I see that global buckling number I don't see those numbers that we were talking about a minute ago this is Oilers formula right here this is point eight seven seven Oilers formula it's listed in your manual E three dash three you'll find all this on page sixteen point one dash thirty three here's where oilers Oilers formula just went astray because he didn't take into account that the fibers were yielding F critical in this region is point eight seven seven Oiler F critical in this region point six five eight F yield F Oiler multiplied times F sub y if the yield is 50 and mr. Oilers says five million this is a zero anything raised to the zero power is one one times F sub y that makes a lot of sense that's the critical buckling stress on a one inch thick tall wide-blanch what you do with it once you get the critical buckling stress you multiply it times the gross area what does that give you that give you then across sectional strength okay what the nominal strength then and I was just looking for that particular technical term and then to turn it into the design strength which is okay for you to run the piece of you right up to is called the resistance factor okay what is that for a column buckling point nine that's correct point nine you saw why didn't remember all that well you're okay because I hadn't had a quiz yet pretty soon it's gonna matter you say well I don't think so because I'm gonna bring my big old thick hundred dollar book you can find it in the book you're good to go but there's a lot of fees in there if you just flip through you saw there's a fee point six oh six I'll try that one tables for compression members so that you don't have to do all this work all this work is good stuff a lot of useful things they'll tell you the global flexural buckling strength they're on page four dash three twenty two for example that may be in the middle of the table maybe the beginning I don't remember where they are referred to as column load tables that tell you the selected strength they always any of these design aids gonna always include the resistance factor so be careful with that if you work out the strength of your column and you've got the nominal strength there and then you go look in the table they won't be the same because you forgot to put the fee in there you so the tables illustrating the following example I'll take your word fart says he wants to compute the available strength of the compression member of example for two I was a 14 by 74 20 feet long we had already calculated for that 20 foot thing we went and got the minimum radius of gyration about the weak axis 20 foot times 12 divided by the radius of gyration about the yy axis it was a pen-pen column that was a one I'm just reminding you I'm sure you remember all that turn out to be 96.67 what are the units of this thing that's correct she's shaking her head the right direction her head's going like this no units because it's a ratio it's an inches over inches times a factor and the gross area is 21.8 so we page 120 here it's where he repeated all the numbers I wonder where I could grab them and see them he says we have tables for your pleasure for fees of CF critical table 422 don't that's my guess is this is the page that's my page that's his page I got got it coming up on the next page they're only given for integer values of slenderness ratio you can take your choice you can just go ahead and pick out the little bit more severe number or you can interpolate that's not my job to teach you teach you how to interpolate I think did y'all already put your homework problem in there yeah okay well you can give that to her and she can give you the homework problems to hand back here's what the table well this is the table for where I was getting the numbers from there's a 14 by 74 I got a couple of pages of that invariably here is your area here is your x-axis radius of gyration here's your y-axis radius of gyration we took the 2.48 and we calculated k l over r for it here's the table under discussion table 4-22 you must do your own slenderness ratio check just knowing how much stress you can put on a 50 ksi piece of steel doesn't include the fact if that 50 ksi piece of steel has slender elements so you're welcome to use this but the slender element check must be done after you use this to see how strong your column is this is not including the slender elements possibility if the k l over r we got page after page of this that was a 50 ksi piece of steel here's a k l over r is one and I think that's where we're going what was the k l over 96 or something like that so I'm looking for the k l over r of around 96 here we go here's another summary the k l over r was 96.77 I don't want this column that's a loud stress there's phi sub c f critical for 50 ksi steel these are based on the equation 3 2 and 3 3 on this page he knows when you're above or below a break point you remember what the break point was for our for our 50 ksi steel global buckling I mean that's really getting down and dirty to ask you that was 113 in other words if you multiplied 4.71 times the square root of 29,000 ksi divided by 50 ksi you got 113 so that's the break point he knows when the break point occurs so he knows when to use one equation below the break point and he knows when to use one above he knows which one to use our slender this ratio is 96. something right in between 22.6 22.9 to interpolate you get 22.67 including the phi if you'd rather you can just take the lower permitted stress and not bother interpolating and in this class you most certainly can't because like I say not my job to teach you how to interpolate and I know you know how to do it so I don't care so if you just want to go to the nearest the next lighter one the next lesser permitted stress than that would be okay here are more pages where the Kaila raw is higher than 113 and more of them remember no slender element check is being done in these tables now let's see where he went ahead used that maybe it was back on the previous page that's local buckling slender element of web or a flange all right so here's what he got he got out of the table 22.67 interpolating then he says then my final answer for how much loads you can have is area gross remember seeing that 21.8 square inches out of the table times a critical buckling stress we got at the table 22.67 including the fees of C that includes the fee says a real tendency to put another fee on there ought to do that that multiplied together gives you 494 kips of load now we don't know what the load request was but whatever it is has to be less than 494 and I says there's a second set of tables which will include the shape itself rather than just talking about the steel because you still now have to see if the 494 is acceptable by checking slenderness ratios of the web and the flange of that shape this column load table was done by somebody who knows how to do that if they are slender elements he'll do that 18 pages of work for you before he goes into the table because this is not theory learn how to do it today that book you bought there that's do it real world let's get on with it column load tables are in part 4 they're on page 4-16 for example probably the one we're going to use and I got it back in 131e here is a typical well it's not typical it's the one he asked for it's a 14 by 74 again here's your 14 by the 16s are in the preceding pages the 10 buys are in the later pages here's a 14 by 74 this is a loud stress design it's easy to get in the wrong table this is your KL the R is already in there he knows how to calculate the R your length was 20 feet and your K was what one why was it one only one way it'd be a one because the column is what how's it supported and on both ends that's right look at everybody looking at you ugly they're not looking at you ugly because you're brilliant they're looking at you ugly say the longer we wait the less we have to memorize don't answer his questions KL was 20 feet and so all you do is you go across to you find a 14 by 74 and you get same number 495 yes sir the K values I can't know I'm sorry I told you in the last class if you look through there some way thank you I just really and you know I've got it but I don't think I've seen it in this set so we'd have to I'd have to go back to a previous set I will say that as you go through your notes or you go through these notes I've tried everywhere to mark you know where those pages appear all right so 495 is a done deal well wait a minute I don't know if it's a done deal it could be that that has slender elements don't care you said a minute ago you cared well a minute ago I wasn't dealing with the 14 by 74 shape I was just dealing by anybody was made out of 50 ksi steel which incidentally the problem with these tables and a good for anything but 50 ksi steel and when you go to the angles you'll find they don't have anything but 36 ksi steel because that's what we usually use for those kind of things so that's why I know where the breakpoint is and that's why he knows what this number is and that's why our value checked to also because he's obvious this must not have slender elements because if it did this number using that F critical table would give us the wrong answer which we would know that it was going to now you want to know who really does have column problems then elements there's a guy that's got column problems right there if that's made out of 50 ksi steel that little C superscript there means this guy's got slender elements therefore many of these numbers not the short fat ones but the long slender ones are going to be affected these numbers will be changed they'll be reduced because they have local buckling here's here's what he says see it's shaped this slender for compression with S of Y is 50 ksi heavy line indicates Caleb or R equal to a greater than 200 he's saying for heaven's sakes you really shouldn't be working in this region I'm not even going to tell you how much load there's going to carry because it's just not good to be able to carry 500 400 300 kips you're already down to 100 below that he suggests you don't go it's not against the law it's very uneconomical quick review analysis of columns here are your e3 equations e3 1 and e3 2 e3 3 e3 4 one of them gives you a fee one of them gives you this one of them gives you that one gives you below the break point one gives above the break point they're all right there and our notes there they are here are here's table 422 that's a great little table the only problem is it is not going to be able to cover the slenderness slenderness of the elements because you don't know which element you're working with you don't know which one covers all common F sub Y that's what's nice whereas the tables down there they only cover specific F sub Y for those kind of shapes normally used lambda sub R not checked for slender elements but all shapes are covered and this one only a few shapes are covered you go back to those tables you find out they run out of things in a hurry there aren't any 8-bias there aren't any 21 by 50 150 shapes and things like that because they're not commonly used for commons columns why his excuse for not putting another 200 pages and charging you another $50 and give you a dolly with the book the values in the table based on global buckling and these equations local stability is assumed and you must not exceed the slenderness ratios now this is I think badly written above this line he's talking about one thing he's talking about table 4-22 and he says well I told him I was doing that yeah but then you said all those some shapes and so on so you didn't really tell them we're talking a major change in thought here this is table 4-22 and these are out of the column load tables here he's warning you that you got a check for excessive width thickness ratios and here he's talking about the column load tables he says in here the tabulated strength has been computed according to the requirements of members with slender elements and no further checking is needed they're good to go they include that design design becomes quite easy with the tables that's not quite easy very few people on earth can do it but you and me to get an economical shape here's what you do you'll be using table 4-1 and it's on page 4-12 he would like you to design a compression member for a service load of 165 dead 535 live 26 feet long pinned on each end he wants a 992 I don't know is that 50k si steel it better be because I'm not gonna be able to use the tables otherwise I'm gonna find out if that's 50k si steel in the buck that's exactly right and he wants you to pick a 14 by shape so just play in the 14k shapes load 1.2 dead 1.6 live there's your piece of use 1054 kips you got to give me something stronger than that nominally times a resistance factor bigger than that number from the column load tables we go to the column load tables this is the 14 by page I'm gonna start with a ooh I don't like that one oh I don't mind that one what's wrong with this one got slender you don't have to check it's got slender elements you're in the tables where the check has been made and corrections have been made you have to go down to a 26 foot column you need 1054 nope nope nope nope see how they're getting fatter see how they're getting heavier stronger go the next page 26 feet I need 1054 no no no no 1054 that'll work a w14 by 132 look in your book it says a w14 by 145 what he forgot to do was a w14 by 145 used to be the right answer because this number was 1050 in the last in the 13th edition of the AISC manual call them up and ask them why they added a little bit you remember a little while ago where they changed the R design a little bit and they changed the H over 8 sub W a little bit you know I don't know if they got better numbers or what but it doesn't matter if they're gonna let me have the other 10 kips I'll take it if all of a sudden I get to drop a size from 145 to 132 legally and no it won't fall down I'll take it here incidentally is the old edition the old 13th edition look at that 1050 you need but you needed 1054 the addition you can live with a smaller shape now then if I ask you to design something without being stuck in the 14 inch region we just say that this one is 24 feet long and you need a load of 275 the same columns I'd go to 24 feet I'm looking for 275 no no no no no I turned to the next page those were eight buys look at that none of those eight buys worked they were all bummers 275 now I'm in the 10 buys no no no no yes 275 a W 10 by 54 is it does it have slender elements no none of these have slender elements that not that it matters that's still a good number so the lightest one I got so far as a W 10 by 54 remember that now let's go to the 12 buys here the 12 buys 275 no no no no 292 that weighs more I'll stick with the one I had a 10 by 58 let's look in the 14 buys 14 buys made 275 275 there we go 61 that doesn't look like I'm gonna win you know I'll check them all because you never know there's something else may show up but a 14 by that's all they got either that or I got tired of doing it and maybe hopefully check the other ones but they weren't they didn't work there's your lightest column shape right there why didn't you just show me that on the first day we got here in class I could have done that you could have but you wouldn't have any idea in the world what was going on that's why all right see you next time sorry Ben you can ask my guys the dang thing went off 20 times no don't no no I don't know what you're getting ready to turn off but it's it's still recording and if I don't get out gracefully I lose the lecture I'll get it thank you here real hold that back yeah back where we got it from somebody in another class is probably sitting in it


All right, everybody. What is going on? We're sitting in the car park Here at a shopping center somewhere in Melbourne. I have no idea where I am But I'm on the way to go and practice some kicks. Okay today's Saturday tomorrow morning 6 30 a.m I've got my assessment with pro kick. I don't want to turn up there without having kicked the ball that would be Stupid it would be idiotic. Why why put myself through that stress? So today I've come to rebel sport. They don't have any American footballs for whatever reason But I've got this one that I brought with me pumped up And I got my boots and I got my camera, of course I'm going I'm actually gonna head to the field the same field that I'm gonna go to tomorrow morning just to have a quick look You know work out where it is it's 6 40 or 6 30 in the morning. I've got to meet them So I don't want to be late. That's one thing. I don't want to be I'm gonna get there at like 6 15 I've just had to run through this mall with no shoes on I only came with socks And I thought I'd be able to find a rebel sport That's like out on its own or like on a street front or something But this one was right in the middle of bloody mall and I've just ran through it with no shoes on Holding a football with tights. No shorts. I Just got to remember it's not Alice Springs anymore. Anyways guys. I will see you for a kick At this field. I think it's what is it cool? Let me see I better actually have the address. What is it Clifton Park? Brunswick, so let's go. I'll see you there All right, everybody Seems as if we're here. I'm not exactly sure what part of it they use But it looks to be pretty sizable. They've got soccer going on the background there and I'm on a soccer field right now But I don't see any lines for like yards or anything like that. I Think you know what? I think I'm just gonna have a kick around here. I've got my own little field here Let's do it Okay, you know Today's pretty significant might not seem it but it is and that's because If I do attend pro kick Australia This could most likely be The field that we we train it I'll be turning up here tomorrow 615 sharp looking for some other people Must say man these boots are sick the fit The fit is perfect It's feels so nice once you get them on anyway I'm gonna warm up and Start kicking the damn ball Gloves Be realistic if I do play I'll probably be wearing gloves. All right I think these are receiving gloves, but It's all good We'll make do So like I was saying before this is pretty significant, man. I'm gonna be here tomorrow morning. I've wanted to be here for so long I Just need the assessment to go well And I pray that it does I pray it goes well Because then I could be lining myself up to train With the view of going to America Taking up a football scholarship earning a degree having an amazing time the rest is history they say So let's go Okay, we're ready to go. I think it took about six tries, but we finally got our first one our first nice connection And it'll be interesting to see how that looks on camera actually I guess some more Six kicks to get my first good one. I cannot do that tomorrow break number one We're 20 minutes in by the way 20 minutes No, I've purposely Targeted the spiral Because of the fact that I know that a lot of the punters in American football do the spiral and I've never actually, you know Practiced hard to get good at it Whenever I'm trying a spiral punt. It's always 50-50 at best and I need that to be higher So that's why we're here. I know and end on it end over in front by this classic rugby pump. I Know how to do that And if they want me moving out of the pocket, for example, if it comes back the defenders coming at me I know it's gonna be charged Back to the spiral. We cannot beat that kick. I may as well leave now or I'll so never be as happy as I am now That was that was a perfect kick. Absolutely perfect


So, my name's Alex Rothenberg, I'm going to be talking about how not to let the Cocoa API crush your Ruby code and really what I think of it as is, you know, how to make Ruby and Cocoa play nice together. So just a little about me, you know, I work for McKinsey Digital Labs, a consulting company, you find me on Twitter, email, GitHub, all the usual places. But basically, I'm a Rubyist, you know, I came into this space from the Ruby side of the world. And I've been thinking a lot about what it is that I love about Ruby. And really, you know, I think it's in Ruby, we care not just about, you know, getting things to work, but about, you know, making our code clean, easy to deal with, easy to go back to months or years later and, you know, really just having clean code that we can understand and deal with. And so, you know, I follow that and I try to do that as I'm writing web applications. And I, you know, I think, you know, with Rails and with, you know, a lot of stuff in the Ruby community, it's fairly easy to do that in the web space. But then, of course, right a couple of years ago, the iPhone came out. And the iPhone was cool and the iPhone was sexy. And, you know, I really wanted to learn how to write iPhone apps.   So, you know, I got Xcode, I got, you know, all sorts of guidelines for, you know, for how to build iOS apps. And, you know, I set out to build this. And I got something that, you know, sort of kind of mostly worked. But behind the scenes, you know, it was a big ball of mess. You know, it was a disaster back there. And, you know, really what it was was, you know, there were all these different things that I knew nothing about and was trying to learn all of them at once.   So I was fighting it all the way. So basically I put that aside, went back to building web apps for a while. And then all of a sudden, you know, Laurent came along and Ruby Motion came out.  So, right, we could use Ruby, use the editor I wanted, not the one Apple, you know, forced on me. And I still had to deal with Cocoa, but I figured I could do that, right? It was just one thing to get into, even though it has these crazy long method names that we all have to fight. So really, this is what I want to talk about today.  And what I learned, you know, as I started, was, you know, my apps started to feel like Cocoa apps that happened to be written in Ruby, which was not really where I wanted to go and what I wanted to do, right? That was back to a big ball of mess. I wanted to get much more, where I was writing Ruby apps that happened to be using the Cocoa API. So the app I'm going to talk about today was, is really serving an address book app that we were building. We didn't make the built-in contact app, but, you know, it was a corporate address book, had our own database of people, and had some other functionality that we wanted to do custom. So, right, so the first thing, you know, I learned about Cocoa. It's just an MVC framework, right? In spite of all those extra letters Colin was adding yesterday, it's really just an MVC framework. So, right, we've all, you know, seen this, right? View controller, lays out views. And you can start, when you first start, right, this is very simple. You can read this, you can see what's going on. Just setting a screen with a white background. And again, right, you know, coming at it from the outside, right, this is what, where the iPhone was cool and sexy, right?  You know, silly as the sounds, this is super exciting on day one. So then I started to read, you know, learn a little more about how you lay out different apps and how you stick views on there. And most of the guidelines were taking me down to the interface builder road, you know, back into Xcode where I didn't want to go. There's a small set of guides that talked about, you know, you could lay out views and code. So that's the road I went down, right? I found a nice tutorial. I found a nice tutorial I was going to follow. Right, it's not that hard to lay out views and code. You just stick a UI label on the screen, give it some text, and boom, right now I got my name up on the screen. So just continuing down this road, you know, I wanted to add my title, right? You could add a title. Not too hard, just another UI view. I wanted to add an email, right? You keep going down this road. You can see it's beginning to get a little bit more messy. I had to shrink the font down to fit it on the screen. And now there's, you know, big blocks of code, kind of hard to figure out what's going on. So, you know, following this tutorial, not a problem, just add some comments, right? Say what each block is doing. So I'm going down this road. I keep going down this road, right? I wanted to add phone number, address. Now the UI is a little messy, right? There's a lot going on there. I need to add some labels, see what's going on. And at this point, you can see, right, this is too small to read up here. And it's too small to read when it's on my screen, right? It's too small to see what's going on. There's just too much going on here. Now, this is really a mess. Something had to stop. So, at this point, I realized I had to take a step back and go back to sort of, you know, first principles. What is it about Ruby? How do we write good Ruby code? So for this, I know Sandy Metz, you know, her name came up a couple times yesterday, but the Putter book is a great book. It just talks about, you know, some very basic ideas. How to write good object-oriented software.  Just, you know, good ideas. So if you guys don't have this book or haven't heard of this book, you should go out and buy it. It's a great book. And one of the things she, you know, talked about and this, you know, came up yesterday was these rules that, you know, I think she talked about this after writing the book, but the basic idea, right, that your classes should be less than 100 lines, methods should be less than five lines, and try not to have any more than four parameters in a method. And these numbers, right, they aren't magic numbers. You know, there's no huge difference, really, if we think about it, between 99 lines and 101 lines. But just sort of the limiting factor of having a number and trying to keep things small just helps, right? Just to have some number that you try and keep things smaller then, helps you keep your code small and focused and easier to read, easier to maintain, cleaner code. So if we just go back to our example, you know, obviously this is not the five-line method here, right? This is something huge and crazy. So luckily, you know, we have a way to deal with this. You know, we have refactoring.   And so to me, this is just, you know, this code's beginning to speak to me. You know, just looking at it, I can see, you know, first I'm going to add the name, then I'm going to add the title, and so on and so on. And, you know, it has the added benefit of the code is really self-documenting now, right? I don't need those comments which saying, you know, add the name now, add the title, because the names of the methods are really doing that same job. Now, of course, you know, with this, you know, we haven't gotten rid of any of that mess. We've just moved stuff around a bit. So we still do have, you know, all that mess and things like add name. And we'll get to that in a second. But we're sort of beginning down the road of, you know, cleaning up the mess that we just created a couple seconds ago, a couple minutes ago. So sort of following the let's get small idea, you know, we can dig into this method and figure out what's going on. So there was a lot going on in there, and it was hard to see at a glance what was going on. But if we really think about it, there were really, you know, two things we're doing. We're just adding the caption, which is that bold text on the left, followed by adding some text. So really, you know, the add name method that we wish we had, you know, would look more like this, you know. It would say, you know, add the caption and then add the text. And now, again, right, this code's beginning to speak to us and tell us what it's doing. And we don't really have to think when we look at it. We just sort of, you know, we see it and we immediately can parse what's going on there. So what is this row view thing we created? And again, it's sort of back to just, you know, basic object-oriented ideas. So, you know, in this case, you know, Coco helps us with this, right? So Coco and in Objective-C, you know, lots of people create custom subclasses of UI View.  You know, create subclasses that do exactly what you want. So the row view is really just the UI View subclass. And its job really is just to encapsulate the fact that it's got two labels inside of it. And the labels just sort of live somewhere on the screen and the caption just, you know, a little bit of styling applied to it. But the real magic of this row view is the fact that it encapsulates the concept of having a caption and having a text. So it sort of, it exposes these two properties to us and hides the fact that really, you know, when you set the caption, you're setting a text property on a label. You know, it lets us from the outside world just think of setting a caption and that detail is all hidden away. So it really lets us get back to, you know, in the viewDidLoad, that really simple, you know, couple lines that speak to us. And then each of the submethods we create, again, a couple simple lines. You know, in this case, we meet our, you know, the arbitrary five lines per method goal. And we have something small that's easy to read and tell what's going on. So for me, the revelation here was just remembering that, you know, as Rubyists, right, we value clarity and we value, you know, keeping our code small and easy to read. And that, you know, even coming into this, you know, what was for me a new world of iOS development and Cocoa to remember these principles and to keep, you know, to keep following these principles. So I think the next thing I realized as I was going through Cocoa is that large part, right, Cocoa was built for Objective-C and Objective-C actually is a super set of C. So there's parts of Cocoa that are nice and object-oriented, like the UI view and, you know, view controller you can deal with in a fairly natural way from Ruby Motion. But there are also big parts that really expose a lot of the underlying C-ness of Cocoa. And, you know, really, you know, the first place that I hit this and, you know, I hit this the most was dealing with, you know, frames, which are really just CG-rex, which is just a C data structure. And the way you're supposed to create them is with the CG-rex-make function. And I think, you know, I imagine, you know, it felt unnatural enough and painful enough as Laurent was building the first versions of Ruby Motion that he gave us this nice, you know, convenience where you can just pass lists of lists into a view when you're setting its frame. And that works fantastic. But the problem is once it's set in the frame you have to actually go into the C data structure to access, to query, you know, what's the, you know, top of the view? You have to say view.frame.origin.y. And the same with, you know, left, tight width, all those things, where really, you know, what I wanted to do, you know, was not have these little mini train-rex scattered throughout my code, but just, you know, ask the view, what's your top, what's your left? Something simple like that. So this was sort of my next revelation to do this, that in Ruby, you know, classes are always open. So we could just monkey patch UI view to, you know, if we want a top method we can just give ourselves a top method. Something nice and easy to work with. And the same applies, you know, even, you know, it becomes even more important when you're dealing with assignments. So let's say we want to just move the view all the way to the left side of the screen. You know, you would think the way, you know, I thought the way to do it was I want to just assign the view.frame.argin.x to zero. You know, unfortunately this never worked for me, so I actually had to reassign the entire frame.  When I look at this, I have absolutely no idea what this code is doing, right? There's just a huge amount of noise and a huge amount of stuff going on. You know, in reality it's just that one zero there that matters. You know, we're changing the x property to zero. Everything else is, you know, stay the same as you were before. So of course, right, we can do the same trick. Right, monkey patch, we can give ourselves a left equals method if we want that hides all that inside. So now this is one of the first things I do when I start a new RubyMotion project is I have this file of, you know, the UIView monkey patches that I copy into my project that gives me all these nice convenience methods.  And now outside of this one place, I can think in terms of, you know, view.top, view.left, and start, you know, having a clean application at the cost of writing this one monkey patch file.  The lesson sort of I learned from this was that as Rubyists, we love DSLs, and that if something is ugly or clunky or hard to use, you know, we can extend it, right? We don't have to use a hard-to-use clumsy interface. We can give ourselves a nicer, cleaner interface to work with. So I think the, you know, the last big challenge we had in our project was, you know, we're building a separate address book application, and that worked great, right? We could have exactly the functionality we wanted, exactly the database of people we wanted, but when my phone rang, you know, Apple's caller ID knew nothing about this, right? So I just got a random phone number. I didn't know who was calling me.  So I looked through the documentation, and, you know, there's this great A-B address book class, you know, a nice object-oriented interface to deal with address books and people, and I was really happy, right? This was going to be nice and easy, but then I, you know, read the next line down and it turned out, right, that's only available on OSX. On iOS, I was stuck back at this, you know, A-B address book framework, which took me a while to figure out, you know, that it was different. They're both called A-B address book, but this one is much more of a C-style API. So instead of having a nice object-oriented interface, you know, for example, if you have a person and want to get their first name, you have to call this crazy method, you know. A-B record copy value with a person, with K A-B person first name property. So again, right, these long, crazy, cocoa things, you know, long names, and that thing even gives you back, you know, it's a CF type ref. I forget how you take that and turn it into an actual string, but this was crazy, you know, this was killing me when I started putting this in my code, right? I just, I had the person, I just wanted to ask, you know, give me your first name, that's it. So what to do about this? Well, this is where I think, you know, as a community, right, we've come up with a solution for this, and the answer is right, there's a wrap for that. You know, lots of people have hit, you know, these corners of cocoa there's hard to work with, maybe unnatural from RubyMotion, and we're wrapping them, right? We're coming up with new cleaner interfaces to get at them, they're just easier to work with. So this is my, you know, little contribution to that space, the motion address book gem. So right, so now there's a gem out there that lets us interact with this, you know, much more object-oriented, much more natural interface to deal with address books and people, and so if you want to get a person, you can, you know, just get the system address book, you know, ask it for an array of all the people, and then you want to get someone's first name, just ask them for their first name. You want to change their first name, just assign it, you want to save them, just call save, right? It's a much easier to work with interface. So not only that, but, you know, sort of back to, you know, thinking about Jack's talk that he just gave, you know, it was a great open source experience for me. So I put this gem out there, and all of a sudden people I didn't know, you know, started contributing to it. So this person, Jason May, who I've never met, who I don't think is here, but he, you know, he found it a little bit useful and started expanding on it and, you know, contributing to it. And I'd say at this point he's probably written more of the code in there than I have. So it was just, you know, a great experience of putting something out there and having someone else out on the internet find it useful. And so everyone should do that. Everyone should put code out and just let other people find it useful, and it really is a great feeling. So to really, you know, by doing these couple things, you know, now when I'm writing the code, it feels much more like I am writing a Ruby application that happens to use Coco, right? You know, we're remembering what it is that we care about with Ruby and what it is we care about with, you know, the code that we're writing with Ruby.  So I think what I've, you know, essentially realized, sort of, over this experience of writing, you know, several Ruby motion apps is that Coco is fantastic.  You know, it's got all these controls, animations.  You know, the API itself is clunky. And that, you know, with Ruby motion, you know, we as Ruby, let's now have the power to tap into Coco and tap into iOS development and write Ruby, you know, write iOS applications and, you know, coming soon Android applications. It's fantastic. But it's really, you know, essentially up to all of us to figure out how to make that work. That there are, you know, lots of challenges and lots of, you know, struggles that we, you know, we need to figure out how to make it work.    Who knows? So, thank you guys.


A warm welcome to everybody. Good morning, afternoon, evening, wherever you are in the world. Most importantly, I hope you're safe. And it's been a year now since we've been running our events entirely virtually. The first one of these was April 2020 and it's been a great experience for us at the Open Group. We've been able to reach far more of you at the same time than we would have been able to if we were having face-to-face meetings. But obviously, we hear regularly the question, when are you going to have your face-to-face meetings? Well, obviously, that's out of our hands right now. That depends on many, many factors. But for now, our goal is to give you the highest best quality experience we can of a virtual event. And we have some great stuff to share with you today. Before I leave the topic of the current situation that everybody is in and the pandemic, our thoughts at the Open Group go out to our many, many participants in India right now in particular. We have a team of staff in India as well. And obviously, things are seemingly quite bad there. And I hope that that too will start to look brighter. And in the meantime, please, please, please take care of you and yours. India is a very important place for us at the Open Group. And at these events, we get many, many participants from there. So I hope some of you are still there. And on that note, if you would like to share in the chat where you are joining from, it's always interesting to know. I know that we have people from more than 85 countries registered for the event today. And many have spread all over the world, ones and twos in some countries and many in others. But it's kind of fun to use the chat channel to just let people know where you are and anything else you want to share. But as John said, please use the Q&A channel for questions for speakers, because that's where I'll be looking when I am looking for questions for the speakers from the audience. So it's hard to monitor both. So please use the Q&A for that. So today, our topic for the whole event is digital standards, open digital standards, something that we are working actively on in the Open Group. And every enterprise is going through or is about to go through. If you haven't started yet, it's digital transformation journey. And it is a journey. We hear that over and over again. It's not something you just declare that you're done. But how do you get there as an organization? Because the key is to actually delivering and executing on a transformation like that, where you're changing not just technologies and processes, but fundamental changes in people's roles. The people are so important. And today we're going to focus on professionals who are needed for some of those key activities. And at the Open Group, we are proud of our various certification programs. We have our knowledge-based certification programs, which we're well known for. Things like Togaf and Arcumate and IT for IT and Open Fair. But we also have something called an Open Professions Program. And we're going to hear a bit more about that in the start of the meeting today. And there's no better person for me to start off with than have a chat with my colleague who has been involved in this from the very beginning and still is very much so. So I'm going to start by having a discussion today with my colleague, James Derave. Now, James is Vice President and General Manager for India at the Open Group. Now, he's in that role, he's responsible for developing our membership and helping organizations in India understand the benefits of using standards of the Open Group. But he's also been very closely involved with all the certification and testing activities of the Open Group over the years and indeed our pre-dissocial organization, XOPEN. As well as all the programs developed for other consortia, which is something else that we've done in the past. So today, as I say, we're going to focus on the Open Group Professional Program or the Open Professions Program, which provides a globally recognized, credential enhancing your value and visibility as a professional while enabling your organization to adopt best practices within its career model. So a warm welcome from the Open Group please for my colleague, James Derave. James, are you there? I think I am. Yes, I can hear you and now I can see you. Great background, by the way. Indeed. I hope you're doing well. You're not in India right now. I think you're joining us from home in the UK. I am indeed and my apologies for the creature leaping about on my shoulders on the video is apparently the headrest of my chair. WebEx can't quite filter out. Okay, I'm sure we'll get used to it. Anyway, glad to have you here, James. And as I said, there's nobody better I could start off the day with in setting the context for our Open Professions Program, but I want to take it back a notch first or back to basics. We talk about professions. What is a profession? It's such a good question.   But the history is very deep. And it goes back to a time when societies were struggling with who to trust to do things, in particular, who do you want to trust to take a knife to cut your leg off. If you need your leg cut off, for example. And the license is given to surgeons to do that. And the part of the deal on giving them the license to commit what would otherwise be a crime is that we have confidence in them. We trust them that they've built up a body of knowledge. They've acquired that knowledge. They've gone through some kind of a training exercise probably early years, it would have been an apprenticeship. These it's more likely to be years of practice in a hospital working with other surgeons being supported being mentored being, you know, having some oversight as they take on more and more responsibility as they become more adept at their profession. So the society gives them essentially a monopoly for wielding that knife, because we trust them. And we don't just trust the people. We trust that whole system by which they became qualified to be a medical professional. So we trust the education we trust the standards that define what a medical profession needs professional needs to be. We trust the assessment and certification methods used by the profession to determine whether someone qualifies to have those letters after their name. And then we'd also trust the ability of the profession to enable people who acquire that qualification to maintain the standard. So there's something about continuing professional development.  And associated also you get other things around that bits bits of infrastructure such as professional indemnity insurance to cope with the fact that professionals need to be accountable for the work they do. So that's that's kind of the history and we all know, we all know doctors it's just part of what we assume a medical practitioner is. But it applies to other professionals such as lawyers or accountants or childhood surveyors or civil engineers or mechanical engineers. But these are all very well established. And I think in, in it, it's different. And it's different for a couple reasons but I think mostly because of because of it well it's new. You know, essentially any since the, well, that's where the earliest in the 50s of any 60 70s the numbers started to go up so we've not been around very long. And so, the other factor in there is the body of knowledge and the established practice of professionals in our, in our industry have been changing very fast over those years. So the cell to mean any consensus about what the body of knowledge is, or about what kind of training and apprenticeship and mentorship is needed so, you know, we're sort of the profession or the community is being sort of scrabbling around to say well where are our foundations how can we build something and that's that's kind of where we've got asked to help out a bit. Right. That's great. Going back to the, the context of the medical profession is a great one for us all to relate to and obviously our day to day world in the open group is quite different but along the way there you mentioned trust standards adhering to standards all of those things. So, so why did we at the open group start our open professions program where did it come from and who's aimed at. Well, you know, one of the things to that may be a little strange when you look at the open group from the outside is, you know, you think there's well there's this organization that does stuff. Well, entirely correct we do, but it's not us as staff that do it, we may enable it to be done. And the intellectual input and creativity and content comes from our members. You know, we were asked by our members to solve the problem of trying to define what a professional initially what a professional architect was. And we thought about it and we asked for input from our members and they said well here's what we think and here's what we think, and we saw an astonishing amount of commonality. So, these were organizations that had spent a lot of time thinking about this problem internally, but rather than having their own definition, they wanted an industry definition of profession and we're prepared to contribute their intellectual property their ideas their thoughts into a common pool. So they asked us to take charge of that and to take it forward turn it into a standard and build what became the professions program. So it was a member request. And the need for doing it was was about not just that they didn't want it to be just their own thing. But they wanted some industry consensus, they want that to be an industry standard for what a professional that stage architect was to be. And they were looking for vending neutrality to add value to that say well it's not a point of phrase is not an HP or an IBM or a cap Gemini definition of what a professional is it's the industry. So that's how we how the program came to be. Right and that that goes, presumably it's that it's the fact that it's built across industry that gives it the credibility and the, which plays to the trust that you talked about with the medical profession that's absolutely, absolutely. And sorry, go ahead. No, no. So that's, that's really why it's why the industry and those who who hire or contract with those professionals believe in the in the program and the credibility of it. Absolutely. And it's not just that, you know, a member consensus came up with the definition of what it needs to be professional they also came up with the definition of how do we find out whether someone meets those criteria. So the process of how someone applies for certification what information must they present how do we evaluate an application. And the, you know, the core feature which is like many other professions is that we use professionals to judge the applying the other professionals who were applying to become professionals within the program. It's not examination. It's by peer review. So final stages into is a review an interview process with a group of certified professionals interviewing a candidate. So, you know, it's it's it mirrors many of the many of those approaches that other professions have used done in a way that we can operate and scale globally. Great. Great. So, we've been we've been doing this for for a few years now. How many, how many professionals do we do we have another program around the world? What's what's the ballpark number? Well, I did look, I must confess, not this morning, but over the weekend, three thousand and eight to two architects, two thousand three hundred and forty three technical specialists, two hundred and fifty one data scientists and four trusted technology practitioners. Right. And the trusted technology ones are most recent, most recent. We're here. We're here more about that. We'll hear more about that later, of course. But so, as I said, the program has been operating for a little while, but we've we've made some changes recently. So what's new. Two big things or are the one really big thing and one one almost big thing for the architects. So we've added another, what we call discipline. So, the program started with just to focus on what we call back in 2006, I think it was it architects and then we've added enterprise architecture and we've added business architecture. And this year we launched digital architecture as a discipline. And that caused us to think very hard about everything we'd ever done. And so, when we define a requirement for an architect, when you go back at look at the words we wrote say five or 10 years ago was often an assumption of a waterfall project in the thinking behind the sentence that described the skill. So we had to look hard at all of those and cut out all the waterfall project style terminology and assumptions about the requirements. And what we found when doing it was that the digital architects actually required nearly all of the same skills as the other other architects, plus a couple of experts, particular ones that were relevant to the digital. So that was big what big change number one we've added digital architect discipline and it's now just available. You can now apply for that to swim. I'm glad to hear that because I told this event. It would be by now so good to know. If you look on the website, they're there, there are forms of that you can start filling them in and I hope you do. Anyway, the other big change was one of the, it was to respond to a criticism that we asked people to fill in a very large form. And we limited people making applications to make to be only 50 to 55 pages long. A lot of work. And we also charged a significant sum of money to make that application. So it caused people a great deal of angst and worry about. Can I expend this amount of effort to keep this application form? And can I risk that amount of time and money to make this application. So in responding to that and I'm trying to make the program a bit more digital in its operation. We have split those applications into multiple sections, which we call milestones. So you can apply for a milestone. And it will be evaluated. And if you get it, you get a milestone badge. You should make the plain badges for achievement of all of these things. And by the time you've got a full set, you then do the final step to apply for certification, which is a small additional increment, which then involves the interviews. So, basically, we've sort of deconstructed, I think that's probably the more modern word to do with this. We've deconstructed it into separate pieces, which when added together. And we've made it up to what we had originally. It's just done in a stepwise fashion to it so that people have smaller steps to climb as they march through their careers. Right, which is, which is important. So they can now do this along the way rather than waiting till they've, they think they've met all the criteria and then looking back. Yeah. Exactly. Exactly. And along the way also means that since a lot of it, a lot of the applications about describing what you did in the project and what skills you demonstrated in the project. You can do one of these applications for an experience milestone, and either during or immediately after the completion of a project, you don't have to wait until you've got a set of three before you apply. So you can do things much closer to the experience, possibly the weekend after. Right. Right. Good. Good. So we're going to, we're going to hear later in this, well, next actually starting next about some of the impact of that and some more detail on the individual parts of the professions but one of the things that that obviously we've been, we've been working on is, is getting the, the program recognized by others so can you, can you talk to, to what extent it's, it's acknowledged beyond the open group. Yes, indeed. And, and, and I wish I could tell you that every country in the world, the government has a profession's recognition register or more you were on the register doesn't exist. There's, there's, you know, the valiant efforts and successful efforts in organ in, in, in, you know, in the European Union for cross recognition of professional qualifications. So, you know, if you're, if you're an accountant in France, you can practice in that anyway. That doesn't exist globally. So we have gone for building recognition with the organizations that seem to have the largest footprint initially. And in this area, it's the British Computer Society, the BCS, we have achieved recognition of all four of our professions at what we call level to master level. They are recognized as meeting all of the qualifications necessary to achieve the BCS is charted it professional professional status. And it's a validation that well established charted professional body in the UK recognizes what we're doing is being equivalent to what they do. So, you know, the moment I can find targets to talk to to have similar conversations in other countries, we will have those conversations. We're, we're certainly aware of them, but the conversations aren't easy because they sell them a well established profession to have this conversation with. We did try and talk to as an organization in which all of these professional bodies globally connect. So we've had conversations like that. You know, could we do a recognition with I fit but that's not born fruition yet. I still have hopes. Right. Okay. And lastly, because we have we have just under two minutes. I mentioned something very important here, which is what you mentioned level two. One of the features of the program is there are different levels that you can you can apply for and ideally move along the move along the path. Can you just say a short one minute version about those. Yeah. 50 second level one is for team members contributing professionals. They may perform and work with support or mentoring.  People joining through to becoming independent practitioners go through a period where they're where they're watch their shepherds that supported their mentors and guided. So that's our level one. Level two is people who master the state of the art who led their projects. And level three is for individuals who are having a significant impact upon the business of their employers or clients. They're making significant change. That's probably how it is. In a nutshell, that's wonderful. Thank you, James. And I will see you later, I believe, for the for the panel discussion. And if, if any of you have questions about program for James, then feed them through the Q and a channel and we'll, we'll pick them up in the panel. And in the meantime, a big virtual round of applause for James to rave. Nice to see you again, James. And we'll move on to our next speaker. Thank you, James.


Hello, welcome back to this lecture on digital communication using GNU radio. My name is Kumar Appaya and I belong to the department of electrical engineering at Haiti Bombay. So, in this lecture we are going to continue from where we left off in the last lecture wherein we are discussing optimal reception in additive white Gaussian noise channel. Before we go to our problem of binary signaling, let us just recollect what the tools that we developed in the previous lecture are. In particular, if you consider M-ary signaling in an AWGN channel, you have a vector y is Si plus n. Remember, how do we get these vectors? We get these vectors by projecting them onto the basis signals and you can just treat your signals as vectors. The effective noise that affects your signaling is that vector obtained by projecting the noise onto your basis signals and we said that because of the theorem of irrelevance, the other part of the noise, the n perpendicular does not affect your detection. And so, you have this particular relationship where your vector y that is received is Si plus n, where n is a 0 mean Gaussian noise vector with variance or covariance matrix sigma square i meaning component wise the noises sigma square variance and independent uncorrelated and independent. Now, the ML detection rule that we derived was basically we had to just write the likelihood function which is the Gaussian and we wanted to maximize this. But we said that since the relationship between y and Si essentially appears only in e power minus, the only part that affects you is the y minus Si norm square because it is e power minus y minus Si the norm square if you just substitute in the PDF that you get from this y is equal to Si plus n. And because you have to maximize e power minus norm y minus Si square by choosing over different i's, you just have to minimize norm y minus Si square which is why the ML detection rule just reduces to the minimum distance detection rule. And we also added a simplification if you want to write it in terms of inner products you can expand this norm y minus Si square, this is a common norm y square term that you can eliminate and put a negative sign. So, you have this to be equivalent to arg max norm y minus sorry inner product y Si minus norm Si square. This is an these two are basically equivalent and you can use either sometimes one will be easier than the other. For the minimum probability of error the only difference is that when you write the likelihood function the prior probability pi i also comes in which is why you have this particular extra term coming in and in the expansion also this will be there. If this log pi i is equal for all i then this arg max is not going to depend on pi i because pi i is something which is not dependent on i therefore this will reduce to the ML. So the ML and minimum probability of error are equivalent and under the case of equally likely transmitted symbols. To give you an idea as to why this actually matters suppose that there is a scenario where one symbol has much higher probability let us say that the probability of sending 1 is 0.9 and the probability of sending 0 is 0.1. I will give you a simple exercise think about this the probability of sending 1 is 0.9 which means at the receiver if you just close your eyes and say always one was sent one was sent one was sent you are going to be right 90 percent of the time. So in this situation you can definitely see that doing ML is not optimal and you have and this MPE if you actually work it out will give you a probability of success of a little more than 0.9. So that is an exercise which you can look at. The proof for this we saw in the previous class so we will not delve into it again. So today let us focus on binary signaling. Binary signaling is something that is like a very basic kind of ingredient it is you can think of it as the act of sending bits but it will also serve as a building block for a higher number of signals. To understand binary signaling and the performance but with binary signaling we will consider the simple case of on off signaling. In this situation either you switch on the voltage and you send a signal or you just send nothing that is these are the two modes it is almost like you know a 0 or a 1 that is basically the model with which we are sending. We are going to inspect only one symbol although you can imagine that this symbol this transmission is going to be repeated again and again and again for every symbol interval capital T as you saw in the pulse shaping related discussion. So in this case let us take this scenario H1 situation where Y is equal to S of t plus N of t that is S of t is sent and Y of t is received this Y of t is S of t plus N of t. This situation is where let us say this is the situation we send 1 this is situation where you send the bit 0 you send nothing Y of t is N of t that is if you do not send anything at the receiver you are only measuring the noise. Now we want to use our the knowledge that we have gained by you know we have proved the optimal detection mechanism and we are going to assume that the 1 and 0 are equally likely. So minimum probability of error is the same as the maximum likelihood. So what we are going to do is we are going to find the optimal detector and when we closed in the last class we guessed that if we look at this inner product YS as a just the number it is by which we are going to use to make our decision the decision rule essentially becomes is this Z more or less than norm S square by 2 this is the guess that we made for good reason because you know this norm YS when there is no noise this inner product YS rather when there is no noise is going to be norm S square when there is no noise and you send 0 then it is going to be 0. So it is like we are guessing that it is the midpoint ok. So that is basically what we are getting at and then we will look at the ML error probabilities and so on in this situation after checking whether this is the correct kind of decision region or decision criterion that we have. Whenever we go into it for every problem till you get comfortable it is a good idea to just match this with our vector picture and what kind of signaling is happening. In this case we have only S of t as our signal of interest. So this S of t can be anything let us say that S of t is something like you know this particular pulse it is like 0 sorry let me just correct that. So let us say our S of t is something like between 0 and 1 it is 1 you can take this you can take a sync you can take anything but for simplicity I am taking this. Now the way I have taken S of t is to say that I have just taken this as my you know the signal if you now want to do something like Gram-Schmidt orthonormalization it is very easy because you only need to do the first step because there is only one signal so the S of t is going to be equal to your psi of t or if you want to just have some fun you can you know you can you need not take this as one you can take this as 10 in which case your S of you know psi of t will be S of t will be psi of t by 10 and so on. So imagine that there is a signal in the background there is a basis in the background this basis is going to be psi of t is equal to S of t by norm S obviously because if you just take S of t and divide it by root of integral S square of t dt this is psi of t is just S of t scaled to be unit energy. So that is the picture that you should have here we have one dimensional signaling because there is only one S of t if there were S 1 of t S 2 of t and if they were in different dimensions you could have had multiple dimension signaling but in this case we have one dimensional signaling fine let us actually now just work this out in a rather neat way and find out this decision whether this decision rule is correct and so on.  So let us take the blue color now let us take the black color let us actually sketch the probability density functions of y under the hypothesis H 0 and under the hypothesis H 1 under the hypothesis H 0 nothing is sent only noise is received under the hypothesis H 1 S of t is sent plus noise is added and that is what is received these are projected onto well in this case you know if you check what we did you had this S of you had just this in an angle bracket y S. So you are essentially just going to add this you are just going to take the inner product with S so we are going to start with that picture ok. So if you send nothing you are going to get something like this this is basically under the hypothesis H 0 if you send and by the way this is the probability density function of Z. So we are going to write this as F Z given dot of Z given dot where dot is H 0 or H 1 that is this is the PDF of Z and this is the PDF of Z under H 1 and this particular point is going to be the mean of Z when H 1 is sent. So let us write those things down. So Z given H 0 that is inner product y comma 0 is 0 I have to write expectation rather ok. Let me just take this a little more slowly so that you can get a better idea. So let me erase this part ok. So now the question is what are the means and variances of these two Gaussians. So first of all why are these Gaussians S because S of t is a known signal if you take S of t plus N of t and if you then convert them to numbers like you just you are just doing Z is equal to angle bracket y comma S ok. So under let us say under H 0 ok Z is equal to angle bracket y comma this is under H 1 of course angle bracket y comma 0 ok which is equal to 0 no but this there is a slight catch this is only in the situation where there is no noise. So you have to ok this is under the case where there is noise because this is actually S plus ok let me erase this this is S plus N sorry N comma 0 which is equal to 0. The other thing we are going to do is we are going to say under H 1 Z is equal to angle bracket y comma S which is equal to inner product S plus N comma S which is equal to inner product N comma S. So this is the situation that we have ok that is if we assume that only nothing is sent we measure the noise if we assume that something is sent we have to measure the we will be measuring S plus N. So now once we go back we have these two scenarios and we will we will find the ML error probabilities by looking at the value of Z but before that let us first just get some things clear which we have written Z is conditionally Gaussian why because you are adding a fixed number if you take inner product y comma S y has N of t that is the Gaussian and all others are fixed numbers. So expectation of Z given at 0 is expectation of angle bracket N comma S which is 0 and variance of Z given at 0 is covariance of NS NS this is something we have seen earlier this sigma square norm S square expectation of Z given H 1 is expectation of SN S plus N comma S which is norm S square similarly variance of Z given H x 1 is covariance of S plus N comma S S plus N comma S again by using our result that you know if you take inner product N v 1 and v 2 you can get this this is something which we will prove. So let us first go back and get those results over here. So just for simplicity I am just going to write them in a in a in a nice way. So what do we have? Okay our definition is Z is inner product y comma S so this Z is a random variable why because it is dependent on N. So now let us say expectation of Z given H 0 what does that mean under H 0 what is the value of y? y is this is expectation of under H 0 y is just N of t. So this is going to be angle bracket N comma S. So this is not at all surprising because you only measure noise and Z has only the noise component overlapped with S and if you write the integral and take the expectation inside that is this is going to be expectation of integral let us say minus infinity infinity more general case S of t N of t dt and if you take the expectation inside this is going to be integral minus infinity to infinity S of t expectation N of t dt this is 0 because expectation of t is 0 because your noise was 0 mean. I am going to leave this as is okay but I am not going to repeat these integrals for the other cases. Now since we need to find the error probability also we need to characterize this Gaussian under H 0 more carefully. So the mean as I have drawn is around 0. So this guess was correct what about the variance how fat is this Gaussian? For that we need to find out the variance of Z given H 0 to do this remember that we had this result the result was expectation of inner product N comma V 1 inner product N comma V 2 where V 1 and V 2 are any 2 fixed signals is equal to sigma square times in angle bracket of V 1 comma V 2. We derived this 2 lectures ago this result will come in handy when we do the work below. So variance of Z given H 0 is see what is Z under hypothesis H 0 it is S plus N sorry it is just you know sorry Y is just N. This is expectation of angle bracket N comma S N comma S okay that is just expectation of N comma S N comma S actually you can maybe rather than write it as expectation let me just write it as covariance because it will be easier for us to use this formula you know that covariance of X comma X is the variance. So I am just writing this as covariance angle bracket N comma S angle bracket N comma S is a real signal. So I can change the order of the covariances I have this formula here. So this gives me sigma square times angle bracket S comma S which is equal to sigma square times norm S square. This means that the covariance of this particular Gaussian under hypothesis H 0 that is a distribution of Z is completely characterized by this when 0 is sent you have the Gaussian to have mean 0 and it has a variance of sigma square norm S square. So that is basically the full characterization of the PDF of Z under the hypothesis H 0 which is another way of saying 0 was sent. Our next task is to repeat this for H 1 okay. So now under H 1 our references that Y of t is S of t plus N of t. So our Z is equal to angle bracket Y plus N comma S which is equal to angle bracket sorry it is not Y plus N it should be S plus N okay because Y is S plus N yeah which is equal to angle bracket SS plus angle bracket NS which is equal to norm S square plus angle bracket N comma S fine. What is the expectation of Z under the hypothesis H 1 you just put your expectation here norm S square is a fixed number because this is a deterministic signal. So this is going to be norm S square plus expectation of angle bracket N comma S we just proved above that expectation of N comma S over here is 0. So the same result applies over here. So this is equal to norm S square. So the mean of Z under the hypothesis H 1 is norm S square for the variance variance of Z given H 1 I am just going to use the covariance approach I will write this as curve angle bracket okay. I am just going to write the covariance of Z comma Z that is going to be S plus N comma S comma S plus N comma S okay just for convenience if you want to do it directly there is no problem but now I have this formula the same formula expectation of N v 1, N v 2 sorry if you write expectation of N come v 1, N v 2 that is covariance of N v 1, N v 2 I should have written this as covariance. So I can just address that also actually I can leave it because there is zero mean so it does not matter.  So if you use this particular formula unfortunately here it is not in the same form because there is an extra S here but we can always use the linearity of the inner product and this is covariance of we can write this as inner product S comma S plus inner product N comma S comma inner product S comma S plus inner product N comma S and as you know this is norm S square norm S square these are fixed numbers for the purposes of covariance we can subtract them out. So this is going to be just curve of inner product N comma S comma inner product N comma S which is equal to not surprising sigma square norm S square which is the same as the previous. Therefore our conclusion over here is that this particular Gaussian under the hypothesis H 1 has a mean at norm S square and has the same variance as the other Gaussian. Therefore by symmetry you should be able to safely conclude that this particular point is the midpoint between 0 and norm S square which is norm S square by 2 ok. So now when you want to make a decision how do you decide given why which hypothesis is more likely it turns out that it is very easy it is the you just have to find out which side of norm S square by 2 you are on. If you are on the right side of norm S square by 2 it is more likely that H 1 happened if it is the left more likely that H 0 happened. In other words if you are closer to norm S square if z is closer to norm S square you are better off saying that 1 was sent if z is closer to rather if it is closer to 0 that is to the left of norm S square by 2 you are better off saying that 0 was sent. This is the optimal decision for this kind of binary signaling but and this is where you know our slide comes in. So, we use the fact that the under hypothesis under hypothesis H 0 z has 0 mean and z has sigma square norm S square variance under hypothesis H 1 z has norm S square as mean and the same thing as variance. Now we have the recipe for making the correct decision. Now unfortunately even with correct decisions we can make or rather not with correct decisions what we think are correct decisions there can be errors why it could so happen that the noise can essentially and even under hypothesis H 0 let us say 0 was sent noise can carry you through to the right side of norm S square by 2. In a similar fashion 1 was sent and there may be a high negative realization of noise that may carry you to the left of norm S square by 2 meaning that under both these hypotheses there is a chance that you may end up making an incorrect decision. These incorrect decisions are what we call errors or symbol errors. So, what we want to find out is that under you know in this scenario what is the probability of making symbol errors. Let us do that afresh let us just move to the next page. So, let us say symbol errors. So, we want to find the symbol error probability. So, let us now draw the I will draw with some spacing this is under hypothesis H 0 and let us now in the other color this is under hypothesis H 1 I do not want you to go negative okay and this is our decision region. So, this is norm S square which is the same as mod S you know integral S square of t dt this is mod S square by 2 and this is 0. Now what is the probability of an error let us say under hypothesis H 0 okay this is the mean actually it should come down just bear with me it should actually just come down after this but yeah an error happens if you send 0 but you fall into this particular region you fall into this particular region. So, there is a symbol error probability that you can find out by finding the probability that under H 0 what is the probability that you cross S square by 2. So, let us now evaluate that probability okay. So, to do that under H 0 remember whatever z parameters are under H 0 it is 0 mean and has sigma square norm S square as the variance. Therefore, if you have sigma square norm S square as the variance then what you need to do is you need to do this probability of error under hypothesis 0 which I write as P is 0 is equal to integral norm S square by 2 to infinity because I want to find this area 1 upon variance root variance is sigma norm S root 2 pi I am writing the formula for Gaussian if you remember it is 1 by sigma root 2 pi e power minus x square by 2 I am just writing sigma norm S root 2 pi e power minus small z square by 2 sigma square norm S square dz this is the formula for the error. How I did I write this because under the hypothesis H 0 mean is 0 variance sigma square norm S square this is the distribution what is the probability under this distribution that the realized random variable falls above norm S square by 2. Let us now evaluate this it should not be too difficult okay because we are good with Gaussians we always want the standard normal to make this the standard normal I am going to make a substitution we are going to say let u is equal to and I am choosing this very carefully it is actually z minus mean of z by root variance mean of z is 0 so z by sigma norm S under this right when z is equal to norm S square by 2 the value of u is so norm S square by 2 so the value of u is going to be so you just substitute norm S square by 2 here you will get norm S by 2 sigma therefore let us now evaluate this integral p e given 0 is equal to integral norm S upon 2 sigma to infinity infinity does not change because it is just a same the same sign it is just a you know scaling by a fixed constant 1 by and if you look at d u is dz upon sigma root S so this particular sigma root S will get absorbed into this dz so you will get root 2 pi e power minus u square by 2 dz. Now your i should perk up over here why because this is actually the q function so this is the q of norm S upon 2 sigma so this q function gives you the probability of having a symbol error when the symbol 0 is sent you can also say bit error because we have 0 and 1 this is the probability of making an error under hypothesis 0 so q of norm S by 2 sigma if you evaluate this you are going to get the answer. Before we talk about this particular some intuitions related to this let us also just look at the probability of error under the hypothesis H 1. So now under hypothesis H 1 it is that you can I am not going to go back and show you but we have seen that the Gaussian which you realize the like the distribution of Z under hypothesis H 1 has a mean of norm S square and a variance of sigma square norm S square and in this situation you make an error if you go to the left of norm S square by 2. Now intuitively because of the symmetry you can clearly see that the area over here is equal to the area over here but still for the first time it is a good idea to evaluate it and verify that it is indeed the case. So, I am just going to write it down quickly and we can confirm that it is going to be the same error probability. So, under hypothesis H 1 we have mean norm S square variance sigma square norm S square. Therefore, our probability of error given 1 is remember we have to be to the left of norm mod S square by 2. So, it is integral minus infinity to mod S square by 2 1 by sigma norm S root 2 pi e power minus we have to be very careful Z minus norm S square the whole square by 2 sigma square norm S square sorry yeah dZ. Now over here again we will make a similar substitution U is equal to Z minus norm S square pi sigma norm S du is equal to dz upon sigma you know norm S that takes care of this part over here and to change the limits when Z is equal to norm S square by 2 u is equal to this norm S square by 2 minus norm S square upon sigma root S. So, this will be minus norm S by sigma ok. This means my p e 1 p e given 1 is going to be just going to go down a little the limits ok the signs do not change nothing changes over here minus infinity to minus norm S by 2 sigma e power minus u square by 2 upon root 2 pi du this is equal to and even though the limit is from minus infinity infinity to minus S by 2 sigma because of the symmetry of the Gaussian it is equivalent to integrating from plus norm S by 2 sigma to infinity this will also be q of norm S upon 2 sigma ok q of norm S upon 2 sigma. Therefore, the probability of error under the hypothesis H 1 and the probability of error under the hypothesis H 0 are both q of norm S by 2 sigma and if since these two are equi-probable the overall probability of symbol error or in this case bit error is going to be half of p e 0 plus half of 1 which is q of norm S by 2 sigma ok. So, this is where we are going to stop for this lecture the key takeaway is that whenever you have this kind of additive white Gaussian noise channel the relationships between the noise and the signal especially in the case of binary signaling will allow you to make these computations very very easily and it is essential for you to understand that wherever possible take advantage of the symmetry to find out the error probabilities easier. You do not always have to work this full thing out sometimes by inspection you may be able to write it, but just be careful. The other thing is whenever you take the metric like z which is angle bracket y comma s to be evaluated evaluating this particular metric and finding the point where you have to make a decision is key. So, to conclude what we said is that under hypothesis H 0 we found the distribution under hypothesis 1 we found the distribution and wherever our decisions actually at norm S square by 2 the value of z being norm square by 2 we cannot make a decision either way of course the probability that the noise will exactly take you there is anyway 0 to the left you will conclude 0 was sent to the right you will conclude 1 was sent. If the noise is very very large then you have to incur symbol errors and this symbol error is given by q of norm S by 2 sigma under the binary signaling approach where it is on off that is a 0 corresponds to 0 being sent and a 1 corresponds to norm S being sent. In the next lecture we will extend this to the concept of binary signaling with two different signals so that you can contrast and compare the effective errors and we will also talk about the energy per symbol and energy per bit and those implications on this kind of signaling. Thank you.