plucky (3) Math::PlanePath::AztecDiamondRings.3pm.gz
NAME
Math::PlanePath::AztecDiamondRings -- rings around an Aztec diamond shape
SYNOPSIS
use Math::PlanePath::AztecDiamondRings;
my $path = Math::PlanePath::AztecDiamondRings->new;
my ($x, $y) = $path->n_to_xy (123);
DESCRIPTION
This path makes rings around an Aztec diamond shape,
46-45 4
/ \
47 29-28 44 3
/ / \ \
48 30 16-15 27 43 ... 2
/ / / \ \ \ \
49 31 17 7--6 14 26 42 62 1
/ / / / \ \ \ \ \
50 32 18 8 2--1 5 13 25 41 61 <- Y=0
| | | | | | | | | |
51 33 19 9 3--4 12 24 40 60 -1
\ \ \ \ / / / /
52 34 20 10-11 23 39 59 -2
\ \ \ / / /
53 35 21-22 38 58 -3
\ \ / /
54 36-37 57 -4
\ /
55-56 -5
^
-5 -4 -3 -2 -1 X=0 1 2 3 4 5
This is similar to the "DiamondSpiral", but has all four corners flattened to 2 vertical or horizontal,
instead of just one in the "DiamondSpiral". This is only a small change to the alignment of numbers in
the sides, but is more symmetric.
Y axis N=1,6,15,28,45,66,etc are the hexagonal numbers k*(2k-1). The hexagonal numbers of the "second
kind" 3,10,21,36,55,78, etc k*(2k+1), are the vertical at X=-1 going downwards. Combining those two is
the triangular numbers 3,6,10,15,21,etc, k*(k+1)/2, alternately on one line and the other. Those are the
positions of all the horizontal steps, ie. where dY=0.
X axis N=1,5,13,25,etc is the "centred square numbers". Those numbers are made by drawing concentric
squares with an extra point on each side each time. The path here grows the same way, adding one extra
point to each of the four sides.
*---*---*---*
| |
| *---*---* | count total "*"s for
| | | | centred square numbers
* | *---* | *
| | | | | |
| * | * | * |
| | | | | |
| | *---* | |
* | | *
| *---*---* |
| |
*---*---*---*
N Start
The default is to number points starting N=1 as shown above. An optional "n_start" can give a different
start, in the same pattern. For example to start at 0,
n_start => 0
45 44
46 28 27 43
47 29 15 14 26 42
48 30 16 6 5 13 25 41
49 31 17 7 1 0 4 12 24 40
50 32 18 8 2 3 11 23 39 59
51 33 19 9 10 22 38 58
52 34 20 21 37 57
53 35 36 56
54 55
FUNCTIONS
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
"$path = Math::PlanePath::AztecDiamondRings->new ()"
"$path = Math::PlanePath::AztecDiamondRings->new (n_start => $n)"
Create and return a new Aztec diamond spiral object.
"($x,$y) = $path->n_to_xy ($n)"
Return the X,Y coordinates of point number $n on the path.
For "$n < 1" the return is an empty list, it being considered the path starts at 1.
"$n = $path->xy_to_n ($x,$y)"
Return the point number for coordinates "$x,$y". $x and $y are each rounded to the nearest integer,
which has the effect of treating each point in the path as a square of side 1, so the entire plane is
covered.
"($n_lo, $n_hi) = $path->rect_to_n_range ($x1,$y1, $x2,$y2)"
The returned range is exact, meaning $n_lo and $n_hi are the smallest and biggest in the rectangle.
FORMULAS
X,Y to N
The path makes lines in each quadrant. The quadrant is determined by the signs of X and Y, then the line
in that quadrant is either d=X+Y or d=X-Y. A quadratic in d gives a starting N for the line and Y (or X
if desired) is an offset from there,
Y>=0 X>=0 d=X+Y N=(2d+2)*d+1 + Y
Y>=0 X<0 d=Y-X N=2d^2 - Y
Y<0 X>=0 d=X-Y N=(2d+2)*d+1 + Y
Y<0 X<0 d=X+Y N=(2d+4)*d+2 - Y
For example
Y=2 X=3 d=2+3=5 N=(2*5+2)*5+1 + 2 = 63
Y=2 X=-1 d=2-(-1)=3 N=2*3*3 - 2 = 16
Y=-1 X=4 d=4-(-1)=5 N=(2*5+2)*5+1 + -1 = 60
Y=-2 X=-3 d=-3+(-2)=-5 N=(2*-5+4)*-5+2 - (-2) = 34
The two X>=0 cases are the same N formula and can be combined with an abs,
X>=0 d=X+abs(Y) N=(2d+2)*d+1 + Y
This works because at Y=0 the last line of one ring joins up to the start of the next. For example N=11
to N=15,
15 2
\
14 1
\
13 <- Y=0
12 -1
/
11 -2
^
X=0 1 2
Rectangle to N Range
Within each row N increases as X increases away from the Y axis, and within each column similarly N
increases as Y increases away from the X axis. So in a rectangle the maximum N is at one of the four
corners of the rectangle.
|
x1,y2 M---|----M x2,y2
| | |
-------O---------
| | |
| | |
x1,y1 M---|----M x1,y1
|
For any two rows y1 and y2, the values in row y2 are all bigger than in y1 if y2>=-y1. This is so even
when y1 and y2 are on the same side of the origin, ie. both positive or both negative.
For any two columns x1 and x2, the values in the part with Y>=0 are all bigger if x2>=-x1, or in the part
of the columns with Y<0 it's x2>=-x1-1. So the biggest corner is at
max_y = (y2 >= -y1 ? y2 ? y1)
max_x = (x2 >= -x1 - (max_y<0) ? x2 : x1)
The difference in the X handling for Y positive or negative is due to the quadrant ordering. When Y>=0,
at X and -X the bigger N is the X negative side, but when Y<0 it's the X positive side.
A similar approach gives the minimum N in a rectangle.
min_y = / y2 if y2 < 0, and set xbase=-1
| y1 if y1 > 0, and set xbase=0
\ 0 otherwise, and set xbase=0
min_x = / x2 if x2 < xbase
| x1 if x1 > xbase
\ xbase otherwise
The minimum row is Y=0, but if that's not in the rectangle then the y2 or y1 top or bottom edge is the
minimum. Then within any row the minimum N is at xbase=0 if Y<0 or xbase=-1 if Y>=0. If that xbase is
not in range then the x2 or x1 left or right edge is the minimum.
OEIS
Entries in Sloane's Online Encyclopedia of Integer Sequences related to this path include
<http://oeis.org/A001844> (etc)
n_start=1 (the default)
A001844 N on X axis, the centred squares 2k(k+1)+1
n_start=0
A046092 N on X axis, 4*triangular
A139277 N on diagonal X=Y
A023532 abs(dY), being 0 if N=k*(k+3)/2
SEE ALSO
Math::PlanePath, Math::PlanePath::DiamondSpiral
HOME PAGE
<http://user42.tuxfamily.org/math-planepath/index.html>
LICENSE
Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 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.
Math-PlanePath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU General Public License along with Math-PlanePath. If not, see
<http://www.gnu.org/licenses/>.