1Math::PlanePath::HexSpiUrsaelrSkCeownetdr(i3b)uted PerlMDaotchu:m:ePnltaanteiPoanth::HexSpiralSkewed(3)
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NAME

6       Math::PlanePath::HexSpiralSkewed -- integer points around a skewed
7       hexagonal spiral
8

SYNOPSIS

10        use Math::PlanePath::HexSpiralSkewed;
11        my $path = Math::PlanePath::HexSpiralSkewed->new;
12        my ($x, $y) = $path->n_to_xy (123);
13

DESCRIPTION

15       This path makes a hexagonal spiral with points skewed so as to fit a
16       square grid and fully cover the plane.
17
18           13--12--11   ...              2
19            |         \   \
20           14   4---3  10  23            1
21            |   |     \   \   \
22           15   5   1---2   9  22    <- Y=0
23             \   \          |   |
24               16   6---7---8  21       -1
25                 \              |
26                   17--18--19--20       -2
27
28            ^   ^   ^   ^   ^   ^
29           -2  -1  X=0  1   2   3  ...
30
31       The kinds of N=3*k^2 numbers which fall on straight lines in the plain
32       "HexSpiral" also fall on straight lines when skewed.  See
33       Math::PlanePath::HexSpiral for notes on this.
34
35   Skew
36       The skewed path is the same shape as the plain "HexSpiral", but fits
37       more points on a square grid.  The skew pushes the top horizontal to
38       the left, as shown by the following parts, and the bottom horizontal is
39       similarly skewed but to the right.
40
41           HexSpiralSkewed               HexSpiral
42
43           13--12--11                   13--12--11
44            |         \                /          \
45           14          10            14            10
46            |             \         /                \
47           15               9     15                   9
48
49           -2  -1  X=0  1   2     -4 -3 -2  X=0  2  3  4
50
51       In general the coordinates can be converted each way by
52
53           plain X,Y -> skewed (X-Y)/2, Y
54
55           skewed X,Y -> plain 2*X+Y, Y
56

Corners

58       "HexSpiralSkewed" is similar to the "SquareSpiral" but cuts off the
59       top-right and bottom-left corners so that each loop is 6 steps longer
60       than the previous, whereas for the "SquareSpiral" it's 8.  See
61       "Corners" in Math::PlanePath::SquareSpiral for other corner cutting.
62
63   Wider
64       An optional "wider" parameter makes the path wider, stretched along the
65       top and bottom horizontals.  For example
66
67           $path = Math::PlanePath::HexSpiralSkewed->new (wider => 2);
68
69       gives
70
71           21--20--19--18--17                    2
72            |                 \
73           22   8---7---6---5  16                1
74            |   |             \   \
75           23   9   1---2---3---4  15        <- Y=0
76             \   \                  |
77              24   10--11--12--13--14  ...      -1
78                 \                      |
79                   25--26--27--28--29--30       -2
80
81            ^   ^   ^   ^   ^   ^   ^   ^
82           -4  -3  -2  -1  X=0  1   2   3  ...
83
84       The centre horizontal from N=1 is extended by "wider" many further
85       places, then the path loops around that shape.  The starting point 1 is
86       shifted to the left by wider/2 places (rounded up to an integer) to
87       keep the spiral centred on the origin X=0,Y=0.
88
89       Each loop is still 6 longer than the previous, since the widening is
90       basically a constant amount added into each loop.  The result is the
91       same as the plain "HexSpiral" of the same widening too.  The effect
92       looks better in the plain "HexSpiral".
93
94   N Start
95       The default is to number points starting N=1 as shown above.  An
96       optional "n_start" can give a different start with the same shape etc.
97       For example to start at 0,
98
99           n_start => 0
100
101           27  26  25  24                            3
102           28  12  11  10  23                        2
103           29  13   3   2   9  22                    1
104           30  14   4   0   1   8  21 ...       <- Y=0
105               31  15   5   6   7  20  39           -1
106                   32  16  17  18  19  38           -2
107                       33  34  35  36  37           -3
108
109           -3  -2  -1  X=0  1   2   3   4
110
111       In this numbering the X axis N=0,1,8,21,etc is the octagonal numbers
112       3*X*(X+1).
113

FUNCTIONS

115       See "FUNCTIONS" in Math::PlanePath for behaviour common to all path
116       classes.
117
118       "$path = Math::PlanePath::HexSpiralSkewed->new ()"
119       "$path = Math::PlanePath::HexSpiralSkewed->new (wider => $w)"
120           Create and return a new hexagon spiral object.  An optional "wider"
121           parameter widens the spiral path, it defaults to 0 which is no
122           widening.
123
124       "$n = $path->xy_to_n ($x,$y)"
125           Return the point number for coordinates "$x,$y".  $x and $y are
126           each rounded to the nearest integer, which has the effect of
127           treating each point in the path as a square of side 1.
128

OEIS

130       Entries in Sloane's Online Encyclopedia of Integer Sequences related to
131       this path include
132
133           <http://oeis.org/A056105> (etc)
134
135           A056105    N on X axis, 3n^2-2n+1
136           A056106    N on Y axis, 3n^2-n+1
137           A056107    N on North-West diagonal, 3n^2+1
138           A056108    N on X negative axis, 3n^2+n+1
139           A056109    N on Y negative axis, 3n^2+2n+1
140           A003215    N on South-East diagonal, centred hexagonals
141
142           n_start=0
143             A000567    N on X axis, octagonal numbers
144             A049450    N on Y axis
145             A049451    N on X negative axis
146             A045944    N on Y negative axis, octagonal numbers second kind
147             A062783    N on X=Y diagonal north-east
148             A033428    N on north-west diagonal, 3*k^2
149             A063436    N on south-west diagonal
150             A028896    N on south-east diagonal
151

SEE ALSO

153       Math::PlanePath, Math::PlanePath::HexSpiral,
154       Math::PlanePath::HeptSpiralSkewed, Math::PlanePath::PentSpiralSkewed,
155       Math::PlanePath::DiamondSpiral
156

HOME PAGE

158       <http://user42.tuxfamily.org/math-planepath/index.html>
159

LICENSE

161       Copyright 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018 Kevin
162       Ryde
163
164       This file is part of Math-PlanePath.
165
166       Math-PlanePath is free software; you can redistribute it and/or modify
167       it under the terms of the GNU General Public License as published by
168       the Free Software Foundation; either version 3, or (at your option) any
169       later version.
170
171       Math-PlanePath is distributed in the hope that it will be useful, but
172       WITHOUT ANY WARRANTY; without even the implied warranty of
173       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
174       General Public License for more details.
175
176       You should have received a copy of the GNU General Public License along
177       with Math-PlanePath.  If not, see <http://www.gnu.org/licenses/>.
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181perl v5.30.1                      2020-01-30Math::PlanePath::HexSpiralSkewed(3)
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