Math-Intensive Reports with GNU Emacs and Calc, Part 1

Calc Does Units

Notice that my example kept track of units. It's able to do so because Calc also can perform symbolic algebra (a subject far too large for this small article) and treats the symbol "in" (inches) as an undetermined factor. Special operations are available to convert units. Calc knows about units and their conversion. For example, how many pints does a lake having 11,000 acre-feet of water contain? To find out, I first write out the volume in the given units:

$ WaterVolume := 11000. acre ft $

Now, if I type the expression WaterVolume => and evaluate it, I get this:

$ WaterVolume => 11000. acre ft $

Exactly what I typed in. Next, by putting the cursor over the acre unit, selecting (with j s and <codej m commands) the units expression (11000. acre ft) and invoking u c (units-convert), Calc will ask me what type of unit should be used in the conversion. I respond pt. Then Calc immediately changes the previous expression to this:

$ WaterVolume => 28674925714.3 pt $

Obviously, Calc knows how to convert an acre-foot to pints, and doing so is much quicker than describing it.

You don't have to use units at all if you don't want to. If you carefully define all your units up front and use them consistently throughout your report, Calc won't have to do any units munging. But it is useful for converting weird commercial units; it can be handy for converting, say, gas pipeline flow rates in MMSCFD into pounds mass per second.

More examples of Emacs/Calc magic will be presented in Part 2 of this article.



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