1Math::PlanePath::DivisiUbsleerCoClounmtnrsi(b3u)ted PerlMaDtohc:u:mPelnatnaetPiaotnh::DivisibleColumns(3)
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NAME

6       Math::PlanePath::DivisibleColumns -- X divisible by Y in columns
7

SYNOPSIS

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

DESCRIPTION

14       This path visits points X,Y where X is divisible by Y going by columns
15       from Y=1 to Y<=X.
16
17           18 |                                                      57
18           17 |                                                   51
19           16 |                                                49
20           15 |                                             44
21           14 |                                          40
22           13 |                                       36
23           12 |                                    34
24           11 |                                 28
25           10 |                              26
26            9 |                           22                         56
27            8 |                        19                      48
28            7 |                     15                   39
29            6 |                  13                33                55
30            5 |                9             25             43
31            4 |             7          18          32          47
32            3 |          4       12       21       31       42       54
33            2 |       2     6    11    17    24    30    38    46    53
34            1 |    0  1  3  5  8 10 14 16 20 23 27 29 35 37 41 45 50 52
35           Y=0|
36              +---------------------------------------------------------
37              X=0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18
38
39       Starting N=0 at X=1,Y=1 means the values 1,3,5,8,etc horizontally on
40       Y=1 are the sums
41
42            i=K
43           sum   numdivisors(i)
44            i=1
45
46       The current implementation is fairly slack and is slow on medium to
47       large N.
48

Proper Divisors

50       "divisor_type => 'proper'" gives only proper divisors of X, meaning
51       that Y=X itself is excluded.
52
53            9 |                                                      39
54            8 |                                                33
55            7 |                                          26
56            6 |                                    22                38
57            5 |                              16             29
58            4 |                        11          21          32
59            3 |                   7       13       20       28       37
60            2 |             3     6    10    15    19    25    31    36
61            1 |       0  1  2  4  5  8  9 12 14 17 18 23 24 27 30 34 35
62           Y=0|
63              +---------------------------------------------------------
64              X=0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18
65
66       The pattern is the same, but the X=Y line skipped.  The high line going
67       up is at Y=X/2, when X is even, that being the highest proper divisor.
68
69   N Start
70       The default is to number points starting N=0 as shown above.  An
71       optional "n_start" can give a different start with the same shape,  For
72       example to start at 1,
73
74           n_start => 1
75
76            9 |                           23
77            8 |                        20
78            7 |                     16
79            6 |                  14
80            5 |               10
81            4 |             8          19
82            3 |          5       13       22
83            2 |       3     7    12    18
84            1 |    1  2  4  6  9 11 15 17 21
85           Y=0|
86              +------------------------------
87              X=0  1  2  3  4  5  6  7  8  9
88

FUNCTIONS

90       See "FUNCTIONS" in Math::PlanePath for behaviour common to all path
91       classes.
92
93       "$path = Math::PlanePath::DivisibleColumns->new ()"
94       "$path = Math::PlanePath::DivisibleColumns->new (divisor_type => $str,
95       n_start => $n)"
96           Create and return a new path object.  "divisor_type" (a string) can
97           be
98
99               "all"       (the default)
100               "proper"
101
102       "($x,$y) = $path->n_to_xy ($n)"
103           Return the X,Y coordinates of point number $n on the path.  Points
104           begin at 0 and if "$n < 0" then the return is an empty list.
105

FORMULAS

107   Rectangle to N Range
108       The cumulative divisor count up to and including a given X column can
109       be calculated from the fairly well-known sqrt formula, a sum from 1 to
110       sqrt(X).
111
112           S = floor(sqrt(X))
113                                     /   i=S             \
114           numdivs cumulative = 2 * |   sum  floor(X/i)   | - S^2
115                                     \   i=1             /
116
117       This means the N range for 0 to X can be calculated without working out
118       all each column count up to X.  In the current code if column counts
119       have been worked out then they're used, otherwise this formula.
120

OEIS

122       This pattern is in Sloane's Online Encyclopedia of Integer Sequences in
123       the following forms,
124
125           <http://oeis.org/A061017> (etc)
126
127           n_start=0 (the default)
128             A006218    N on Y=1 row, cumulative count of divisors
129             A077597    N on X=Y diagonal, cumulative count divisors - 1
130
131           n_start=1
132             A061017    X coord, each n appears countdivisors(n) times
133             A027750    Y coord, list divisors of successive k
134             A056538    X/Y, divisors high to low
135
136           divisor_type=proper (and default n_start=0)
137             A027751    Y coord divisor_type=proper, divisors of successive n
138                          (extra initial 1)
139
140           divisor_type=proper, n_start=2
141             A208460    X-Y, being X subtract each proper divisor
142
143       A208460 has "offset" 2, hence "n_start=2" to match that.  The same with
144       all divisors would simply insert an extra 0 for the difference at X=Y.
145

SEE ALSO

147       Math::PlanePath, Math::PlanePath::CoprimeColumns
148

HOME PAGE

150       <http://user42.tuxfamily.org/math-planepath/index.html>
151

LICENSE

153       Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017 Kevin Ryde
154
155       Math-PlanePath is free software; you can redistribute it and/or modify
156       it under the terms of the GNU General Public License as published by
157       the Free Software Foundation; either version 3, or (at your option) any
158       later version.
159
160       Math-PlanePath is distributed in the hope that it will be useful, but
161       WITHOUT ANY WARRANTY; without even the implied warranty of
162       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
163       General Public License for more details.
164
165       You should have received a copy of the GNU General Public License along
166       with Math-PlanePath.  If not, see <http://www.gnu.org/licenses/>.
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170perl v5.28.1                      2017-12-0M3ath::PlanePath::DivisibleColumns(3)
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