Math::PlanePath::Staircase -- integer points in stair-step diagonal stripes
use Math::PlanePath::Staircase; my $path = Math::PlanePath::Staircase->new; my ($x, $y) = $path->n_to_xy (123);
This path makes a staircase pattern down from the Y axis to the X,
8 29 | 7 30---31 | 6 16 32---33 | | 5 17---18 34---35 | | 4 7 19---20 36---37 | | | 3 8--- 9 21---22 38---39 | | | 2 2 10---11 23---24 40... | | | 1 3--- 4 12---13 25---26 | | | Y=0 -> 1 5--- 6 14---15 27---28 ^ X=0 1 2 3 4 5 6
The 1,6,15,28,etc along the X axis at the end of each run are the hexagonal numbers k*(2*k-1). The diagonal 3,10,21,36,etc up from X=0,Y=1 is the second hexagonal numbers k*(2*k+1), formed by extending the hexagonal numbers to negative k. The two together are the triangular numbers k*(k+1)/2.
Legendre's prime generating polynomial 2*k^2+29 bounces around for some low values then makes a steep diagonal upwards from X=19,Y=1, at a slope 3 up for 1 across, but only 2 of each 3 drawn.
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
$path = Math::PlanePath::Staircase->new ()
Create and return a new staircase path object.
($x,$y) = $path->n_to_xy ($n)
Return the X,Y coordinates of point number
$n on the path.
$n < 0.5 the return is an empty list, it being considered the path begins at 1.
$n = $path->xy_to_n ($x,$y)
Return the point number for coordinates
$y are rounded to the nearest integers, which has the effect of treating each point
$n as a square of side 1, so the quadrant x>=-0.5, y>=-0.5 is covered.
($n_lo, $n_hi) = $path->rect_to_n_range ($x1,$y1, $x2,$y2)
The returned range is exact, meaning
$n_hi are the smallest and biggest in the rectangle.
Within each row increasing X is increasing N, and in each column increasing Y is increasing pairs of N. Thus for
rect_to_n_range() the lower left corner vertical pair is the minimum N and the upper right vertical pair is the maximum N.
A given X,Y is the larger of a vertical pair when ((X^Y)&1)==1. If that happens at the lower left corner then it's X,Y+1 which is the smaller N, as long as Y+1 is in the rectangle. Conversely at the top right if ((X^Y)&1)==0 then it's X,Y-1 which is the bigger N, again as long as Y-1 is in the rectangle.
Copyright 2010, 2011, 2012, 2013 Kevin Ryde
This file is part of Math-PlanePath.
Math-PlanePath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.
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