SYNOPSIS
use Math::PlanePath::UlamWarburtonQuarter;
my $path = Math::PlanePath::UlamWarburtonQuarter>new;
my ($x, $y) = $path>n_to_xy (123);
DESCRIPTION
This is the pattern of a cellular automaton studied by Ulam and Warburton, confined to a quarter of the plane and oriented diagonally. Cells are numbered by growth tree row and anticlockwise within the row.
14  81 80 79 78 75 74 73 72 13  57 56 55 54 12  82 48 47 77 76 46 45 71 11  40 39 10  83 49 36 35 34 33 44 70 9  58 28 27 53 8  84 85 37 25 24 32 68 69 7  22 6  20 19 18 17 23 31 67 66 5  12 11 26 52 4  21 9 8 16 29 30 43 65 3  6 38 2  5 4 7 15 59 41 42 64 1  2 10 50 51 Y=0 1 3 13 14 60 61 62 63 + X=0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
The growth rule is a given cell grows diagonally NE, NW, SE and SW, but only if the new cell has no neighbours and is within the first quadrant. So the initial cell ``a'' is N=1,
  a initial cell, depth=0 +
It's confined to the first quadrant so can only grow NE as ``b'',
 b  a "b" depth=1 +
Then the next row ``c'' cells can go in three directions SE, NE, NW. These cells are numbered anticlockwise around from the SE as N=3,N=4,N=5.
 c c  b  a c "c" depth=2 +
The ``d'' cell is then only a single on the leading diagonal, since the other diagonals all already have neighbours (the existing ``c'' cells).
 d  c c depth=3  b  a c +  e e  d  c c e depth=4  b  a c +  f f  e e  d  c c e depth=5  b f  a c +  g g g g  f f  g e e g  d  c c e g depth=6  b f  a c g g +
In general the pattern always always grows by 1 along the X=Y leading diagonal. The point on that diagonal is the middle of row depth=X. The pattern expands into the sides with a selfsimilar diamond shaped pattern filling 6 of 16 cells in any 4x4 square block.
Tree Row Ranges
Counting depth=0 as the N=1 at the origin, depth=1 as the next N=2, etc, the number of new cells added in the tree row is
rowwidth(depth) = 3^(count_1_bits(depth+1)  1)
So depth=0 has 3^(11)=1 cells, as does depth=1 which is N=2. Then depth=2 has 3^(21)=3 cells N=3,N=4,N=5 because depth+1=3=0b11 has two 1 bits in binary. The N row start and end is the cumulative total of those before it,
Ndepth(depth) = 1 + rowwidth(0) + ... + rowwidth(depth1) Nend(depth) = rowwidth(0) + ... + rowwidth(depth)
For example depth=2 ends at N=(1+1+3)=5.
depth Ndepth rowwidth Nend 0 1 1 1 1 2 1 2 2 3 3 5 3 6 1 6 4 7 3 9 5 10 3 12 6 13 9 21 7 22 1 22 8 23 3 25
At row depth+1 = powerof2 the Ndepth sum is
Ndepth(depth) = 1 + (4^a1)/3 for depth+1 = 2^a
For example depth=3 is depth+1=2^2 starts at N=1+(4^21)/3=6, or depth=7 is depth+1=2^3 starts N=1+(4^31)/3=22.
Further bits in the depth+1 contribute powersof4 with a tripling for each bit above it. So if depth+1 has bits a,b,c,d,etc from high to low then
depth+1 = 2^a + 2^b + 2^c + 2^d ... a>b>c>d... Ndepth = 1 + (1 + 4^a + 3 * 4^b + 3^2 * 4^c + 3^3 * 4^d + ...) / 3
For example depth=5 is depth+1=6 = 2^2+2^1 is Ndepth = 1+(4^21)/3 + 4^1 = 10. Or depth=6 is depth+1=7 = 2^2+2^1+2^0 is Ndepth = 1+(4^21)/3 + 4^1 + 3*4^0 = 13.
SelfSimilar Replication
The square shape growth to depth=2^level2 repeats the pattern to the preceding depth=2^(level1)2 three times. For example,
 d d c c depth=6 = 2^32  d c triplicates  d d c c depth=2 = 2^22  *  a a b b  a b  a a b b +
The 3x3 square ``a'' repeats, pointing SE, NE and NW as ``b'', ``c'' and ``d''. This resulting 7x7 square then likewise repeats. The points in the path here are numbered by tree rows rather than by this sort of replication, but the replication helps to see the structure of the pattern.
Octant
Option "parts => 'octant'" confines the pattern to the first eighth of the plane 0<=Y<=X.
parts => "octant" 14  50 13  36 12  31 49 11  26 10  24 30 48 9  19 35 8  17 23 46 47 7  15 6  14 16 22 45 44 5  9 18 34 4  7 13 20 21 29 43 3  5 25 2  4 6 12 37 27 28 42 1  2 8 32 33 Y=0  1 3 10 11 38 39 40 41 + X=0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
In this arrangement N=1,2,4,5,7,etc on the leading diagonal is the last N of each row ("tree_depth_to_n_end()").
Upper Octant
Option "parts => 'octant_up'" confines the pattern to the upper octant 0<=X<=Y of the first quadrant.
parts => "octant_up" 14  46 45 44 43 40 39 38 37 13  35 34 33 32 12  47 30 29 42 41 28 27 11  26 25 10  48 31 23 22 21 20 9  36 19 18 8  49 50 24 17 16 7  15 6  13 12 11 10 5  9 8 4  14 7 6 3  5 2  4 3 1  2 Y=0  1 + X=0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
In this arrangement N=1,2,3,5,6,etc on the leading diagonal is the first N of each row ("tree_depth_to_n()").
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 7  21 6  19 18 17 16 5  11 10 4  20 8 7 15 3  5 2  4 3 6 14 1  1 9 Y=0 0 2 12 13 + X=0 1 2 3 4 5 6 7
FUNCTIONS
See ``FUNCTIONS'' in Math::PlanePath for behaviour common to all path classes. "$path = Math::PlanePath::UlamWarburtonQuarter>new ()"
 "$path = Math::PlanePath::UlamWarburtonQuarter>new (parts => $str, n_start => $n)"

Create and return a new path object. "parts" can be
1 first quadrant, the default "octant" first eighth "octant_up" upper eighth
Tree Methods
 "@n_children = $path>tree_n_children($n)"

Return the children of $n, or an empty list if $n has no children
(including when "$n < 1", ie. before the start of the path).
The children are the cells turned on adjacent to $n at the next row. The way points are numbered means that when there's multiple children they're consecutive N values, for example at N=12 the children 19,20,21.
 "$n_parent = $path>tree_n_parent($n)"
 Return the parent node of $n, or "undef" if "$n <= 1" (the start of the path).
Tree Descriptive Methods
 "@nums = $path>tree_num_children_list()"

Return a list of the possible number of children at the nodes of $path.
This is the set of possible return values from "tree_n_num_children()".
parts tree_num_children_list()   1 0, 1, 3 octant 0, 1, 2, 3 octant_up 0, 1, 2, 3
The octant forms have 2 children when branching from the leading diagonal, otherwise 0,1,3.
Level Methods
 "($n_lo, $n_hi) = $path>level_to_n_range($level)"
 Return "($n_start, tree_depth_to_n_end(2**($level+1)  2))".
OEIS
Entries in Sloane's Online Encyclopedia of Integer Sequences related to this path includes
 <http://oeis.org/A151920> (etc)
parts=1 (the default) A147610 num cells in row, tree_depth_to_width() A151920 total cells to depth, tree_depth_to_n_end() parts=octant,octant_up A079318 num cells in row, tree_depth_to_width()
LICENSE
Copyright 2011, 2012, 2013, 2014, 2015, 2016 Kevin RydeThis file is part of MathPlanePath.
MathPlanePath 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.
MathPlanePath 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 MathPlanePath. If not, see <http://www.gnu.org/licenses/>.