++ed by:

2 PAUSE users

Kevin Ryde


Math::PlanePath::KnightSpiral -- integer points around a square, by chess knight moves


 use Math::PlanePath::KnightSpiral;
 my $path = Math::PlanePath::KnightSpiral->new;


This path traverses the plane by an infinite "knight's tour" in the form of a square spiral.

        21   4   9  14  19                 2
        10  15  20   3   8      28         1
         5  22   1  18  13            <- y=0
        16  11  24   7   2  27             1
        23   6  17  12  25                 2

        -2  -1  x=0  1   2   3

Each step is a chess knight's move 1 across and 2 along, or vice versa. The pattern makes 4 cycles on a 2-wide path around a square before stepping outwards to do the same again to a now bigger square. The above sample shows the first 4-cycle around the central 1, then stepping out at 26 and beginning to go around the outside of the 5x5 square.

An attractive traced out picture of the path can be seen at the following page (quarter way down under "Open Knight's Tour"),

See math-image to draw the path lines too.



$path = Math::PlanePath::KnightSpiral->new ()

Create and return a new knight spiral object.





Return the point number for coordinates $x,$y. $x and $y are each rounded to the nearest integer, which has the effect of treating each N in the path as centred in a square of side 1, so the entire plane is covered.


This Knight's tour is in Sloane's OEIS following the Knight spiral and giving the resulting X,Y location by the SquareSpiral numbering. There's eight forms for 4 rotations and spiralling the same or opposite directions.

      A068608   same knight and square spiral directions
      A068609   rotate 90 degrees
      A068610   rotate 180 degrees
      A068611   rotate 270 degrees
      A068612   rotate 180 degrees, spiral opp dir (X negate)
      A068613   rotate 270 degrees, spiral opp dir
      A068614   spiral opposite direction (Y negate)
      A068615   rotate 90 degrees, spiral opp dir (X,Y transpose)

See examples/knights-oeis.pl for a sample program printing the values of A068608.


Math::PlanePath, Math::PlanePath::SquareSpiral




Copyright 2010, 2011, 2012, 2013, 2014 Kevin Ryde

This file is part of Math-PlanePath.


