Math::PlanePath::PyramidSpiral -- integer points drawn around a pyramid
use Math::PlanePath::PyramidSpiral; my $path = Math::PlanePath::PyramidSpiral->new; my ($x, $y) = $path->n_to_xy (123);
This path makes a pyramid shaped spiral,
31 3 / \ 32 13 30 2 / / \ \ 33 14 3 12 29 1 / / / \ \ \ 34 15 4 1--2 11 28 ... <- Y=0 / / / \ \ \ 35 16 5--6--7--8--9-10 27 52 -1 / / \ \ 36 17-18-19-20-21-22-23-24-25-26 51 -2 / \ 37-38-39-40-41-42-43-44-45-46-47-48-49-50 -3 ^ -6 -5 -4 -3 -2 -1 X=0 1 2 3 4 5 6 7
The perfect squares 1,4,9,16 fall one before the bottom left corner of each loop, and the pronic numbers 2,6,12,20,30,etc are the vertical upwards from X=1,Y=0.
This spiral goes around at the same rate as the SquareSpiral
. It's as if two corners are cut off (like the DiamondSpiral
) and two others extended (like the OctagramSpiral
). The net effect is the same looping rate but the points pushed around a bit.
Taking points up to a perfect square shows the similarity. The two triangular cut-off corners marked by "."s are matched by the two triangular extensions.
+--------------------+ 7x7 square | . . . 31 . . .| | . . 32 13 30 . .| | . 33 14 3 12 29 .| |34 15 4 1 2 11 28| 35|16 5 6 7 8 9 10|27 36 17|18 19 20 21 22 23 24|25 26 37 38 39|40 41 42 43 44 45 46|47 48 49 +--------------------+
The default is to number points starting N=1 as shown above. An optional n_start
can give a different start, with the same shape etc. For example to start at 0,
12 n_start => 0 / \ 13 2 11 / / \ \ 14 3 0--1 10 / / \ 15 4--5--6--7--8--9 / 16-17-18-19-20-21-22-...
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
$path = Math::PlanePath::PyramidSpiral->new ()
$path = Math::PlanePath::PyramidSpiral->new (n_start => $n)
Create and return a new pyramid spiral object.
$n = $path->xy_to_n ($x,$y)
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 path is in Sloane's Online Encyclopedia of Integer Sequences as
http://oeis.org/A053615 (etc)
n_start=1 (the default) A053615 abs(X), distance to next pronic, but starts n=0 A054552 N on X axis, 4n^2 - 3n + 1 A033951 N on South-East diagonal, 4n^2 + 3n + 1 A214250 sum N of eight surrounding cells A217013 permutation N of points in SquareSpiral order rotated +90 degrees A217294 inverse
In the two permutations the pyramid spiral is conceived as starting to the left and the square spiral starting upwards. The paths here start in the same direction (both to the right), hence rotate 90 to adjust the orientation.
n_start=0 A001107 N on X axis, decagonal numbers A002939 N on Y axis A033991 N on X negative axis A002943 N on Y negative axis A007742 N on diagonal South-West A033954 N on diagonal South-East, decagonal second kind n_start=2 A185669 N on diagonal South-East
Math::PlanePath, Math::PlanePath::SquareSpiral, Math::PlanePath::PyramidRows, Math::PlanePath::TriangleSpiral, Math::PlanePath::TriangleSpiralSkewed
http://user42.tuxfamily.org/math-planepath/index.html
Copyright 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017 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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