1Math::PlanePath::PyramiUdsReorwsC(o3n)tributed Perl DocuMmaetnht:a:tPiloannePath::PyramidRows(3)
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NAME

6       Math::PlanePath::PyramidRows -- points stacked up in a pyramid
7

SYNOPSIS

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

DESCRIPTION

14       This path arranges points in successively wider rows going upwards so
15       as to form an upside-down pyramid.  The default step is 2, ie. each row
16       2 wider than the preceding, an extra point at the left and the right,
17
18           17  18  19  20  21  22  23  24  25         4
19               10  11  12  13  14  15  16             3
20                    5   6   7   8   9                 2
21                        2   3   4                     1
22                            1                   <-  Y=0
23
24           -4  -3  -2  -1  X=0  1   2   3   4 ...
25
26       The right end N=1,4,9,16,etc is the perfect squares.  The vertical
27       2,6,12,20,etc at x=-1 is the pronic numbers s*(s+1), half way between
28       those successive squares.
29
30       The step 2 is the same as the "PyramidSides", "Corner" and
31       "SacksSpiral" paths.  For the "SacksSpiral", spiral arms going to the
32       right correspond to diagonals in the pyramid, and arms to the left
33       correspond to verticals.
34
35   Step Parameter
36       A "step" parameter controls how much wider each row is than the
37       preceding, to make wider pyramids.  For example step 4
38
39           my $path = Math::PlanePath::PyramidRows->new (step => 4);
40
41       makes each row 2 wider on each side successively
42
43          29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45        4
44                16 17 18 19 20 21 22 23 24 25 26 27 28              3
45                       7  8  9 10 11 12 13 14 15                    2
46                             2  3  4  5  6                          1
47                                   1                          <-  Y=0
48
49                -6 -5 -4 -3 -2 -1 X=0 1  2  3  4  5  6 ...
50
51       If the step is an odd number then the extra is at the right, so step 3
52       gives
53
54           13  14  15  16  17  18  19  20  21  22        3
55                6   7   8   9  10  11  12                2
56                    2   3   4   5                        1
57                        1                          <-  Y=0
58
59           -3  -2  -1  X=0  1   2   3   4 ...
60
61       Or step 1 goes solely to the right.  This is equivalent to the
62       Diagonals path, but columns shifted up to make horizontal rows.
63
64           step => 1
65
66           11  12  13  14  15                4
67            7   8   9  10                    3
68            4   5   6                        2
69            2   3                            1
70            1                          <-  Y=0
71
72           X=0  1   2   3   4 ...
73
74       Step 0 means simply a vertical, each row 1 wide and not increasing.
75       This is unlikely to be much use.  The Rows path with "width" 1 does
76       this too.
77
78           step => 0
79
80            5        4
81            4        3
82            3        2
83            2        1
84            1    <-y=0
85
86           X=0
87
88       Various number sequences fall in regular patterns positions depending
89       on the step.  Large steps are not particularly interesting and quickly
90       become very wide.  A limit might be desirable in a user interface, but
91       there's no limit in the code as such.
92
93   Align Parameter
94       An optional "align" parameter controls how the points are arranged
95       relative to the Y axis.  The default shown above is "centre".
96
97       "right" means points to the right of the axis,
98
99           align=>"right"
100
101           26  27  28  29  30  31  32  33  34  35  36        5
102           17  18  19  20  21  22  23  24  25                4
103           10  11  12  13  14  15  16                        3
104            5   6   7   8   9                                2
105            2   3   4                                        1
106            1                                            <- Y=0
107
108           X=0  1   2   3   4   5   6   7   8   9  10
109
110       "left" is similar but to the left of the Y axis, ie. into negative X.
111
112           align=>"left"
113
114           26  27  28  29  30  31  32  33  34  35  36        5
115                   17  18  19  20  21  22  23  24  25        4
116                           10  11  12  13  14  15  16        3
117                                    5   6   7   8   9        2
118                                            2   3   4        1
119                                                    1    <- Y=0
120
121           -10 -9  -8  -7  -6  -5  -4  -3  -2  -1  X=0
122
123       The step parameter still controls how much longer each row is than its
124       predecessor.
125
126   N Start
127       The default is to number points starting N=1 as shown above.  An
128       optional "n_start" can give a different start, in the same rows
129       sequence.  For example to start at 0,
130
131           n_start => 0
132
133           16 17 18 19 20 21 22 23 24        4
134               9 10 11 12 13 14 15           3
135                  4  5  6  7  8              2
136                     1  2  3                 1
137                        0                <- Y=0
138           --------------------------
139           -4 -3 -2 -1 X=0 1  2  3  4
140
141   Step 3 Pentagonals
142       For step=3 the pentagonal numbers 1,5,12,22,etc, P(k) = (3k-1)*k/2, are
143       at the rightmost end of each row.  The second pentagonal numbers
144       2,7,15,26, S(k) = (3k+1)*k/2 are the vertical at x=-1.  Those second
145       numbers are obtained by P(-k), and the two together are the
146       "generalized pentagonal numbers".
147
148       Both these sequences are composites from 12 and 15 onwards,
149       respectively, and the immediately preceding P(k)-1, P(k)-2, and S(k)-1,
150       S(k)-2 are too.  They factorize simply as
151
152           P(k)   = (3*k-1)*k/2
153           P(k)-1 = (3*k+2)*(k-1)/2
154           P(k)-2 = (3*k-4)*(k-1)/2
155           S(k)   = (3*k+1)*k/2
156           S(k)-1 = (3*k-2)*(k+1)/2
157           S(k)-2 = (3*k+4)*(k-1)/2
158
159       Plotting the primes on a step=3 "PyramidRows" has the second pentagonal
160       S(k),S(k)-1,S(k)-2 as a 3-wide vertical gap of no primes at X=-1,-2,-3.
161       The the plain pentagonal P(k),P(k-1),P(k)-2 are the endmost three N of
162       each row non-prime.  The vertical is much more noticeable in a plot.
163
164              no primes these three columns         no primes these end three
165                except the low 2,7,13                     except low 3,5,11
166                      |  |  |                                /  /  /
167            52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70
168               36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
169                  23 24 25 26 27 28 29 30 31 32 33 34 35
170                     13 14 15 16 17 18 19 20 21 22
171                         6  7  8  9 10 11 12
172                            2  3  4  5
173                               1
174            -6 -5 -4 -3 -2 -1 X=0 1  2  3  4  5  6  7  8  9 10 11 ...
175
176       With align="left" the end values can be put into columns,
177
178                                       no primes these end three
179           align => "left"                  except low 3,5,11
180                                                   |  |  |
181           36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51        5
182                    23 24 25 26 27 28 29 30 31 32 33 34 35        4
183                             13 14 15 16 17 18 19 20 21 22        3
184                                       6  7  8  9 10 11 12        2
185                                                2  3  4  5        1
186                                                         1    <- Y=0
187                     ... -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 X=0
188
189       In general a constant offset S(k)-c is a column and from P(k)-c is a
190       diagonal sloping up dX=2,dY=1 right.  The simple factorizations above
191       using the roots of the quadratic P(k)-c or S(k)-c is possible whenever
192       24*c+1 is a perfect square.  This means the further columns S(k)-5,
193       S(k)-7, S(k)-12, etc also have no primes.
194
195       The columns S(k), S(k)-1, S(k)-2 are prominent because they're
196       adjacent.  There's no other adjacent columns of this type because the
197       squares after 49 are too far apart for 24*c+1 to be a square for
198       successive c.  Of course there could be other reasons for other columns
199       or diagonals to have few or many primes.
200

FUNCTIONS

202       See "FUNCTIONS" in Math::PlanePath for behaviour common to all path
203       classes.
204
205       "$path = Math::PlanePath::PyramidRows->new ()"
206       "$path = Math::PlanePath::PyramidRows->new (step => $integer, align =>
207       $str, n_start => $n)"
208           Create and return a new path object.  The default "step" is 2.
209           "align" is a string, one of
210
211               "centre"    the default
212               "right"     points aligned right of the Y axis
213               "left"      points aligned left of the Y axis
214
215           Points are always numbered from left to right in the rows, the
216           alignment changes where each row begins (or ends).
217
218       "($x,$y) = $path->n_to_xy ($n)"
219           Return the X,Y coordinates of point number $n on the path.
220
221           For "$n <= 0" the return is an empty list since the path starts at
222           N=1.
223
224       "$n = $path->xy_to_n ($x,$y)"
225           Return the point number for coordinates "$x,$y".  $x and $y are
226           each rounded to the nearest integer, which has the effect of
227           treating each point in the pyramid as a square of side 1.  If
228           "$x,$y" is outside the pyramid the return is "undef".
229
230       "($n_lo, $n_hi) = $path->rect_to_n_range ($x1,$y1, $x2,$y2)"
231           The returned range is exact, meaning $n_lo and $n_hi are the
232           smallest and biggest in the rectangle.
233
234   Descriptive Methods
235       "$x = $path->sumxy_minimum()"
236       "$x = $path->sumxy_maximum()"
237           Return the minimum or maximum values taken by coordinate sum X+Y
238           reached by integer N values in the path.  If there's no minimum or
239           maximum then return "undef".
240
241           The path is right and above the X=-Y diagonal, thus giving a
242           minimum sum, in the following cases.
243
244               align      condition for sumxy_minimum=0
245               ------     -----------------------------
246               centre              step <= 3
247               right               always
248               left                step <= 1
249
250       "$x = $path->diffxy_minimum()"
251       "$x = $path->diffxy_maximum()"
252           Return the minimum or maximum values taken by coordinate difference
253           X-Y reached by integer N values in the path.  If there's no minimum
254           or maximum then return "undef".
255
256           The path is left and above the X=Y leading diagonal, thus giving a
257           minimum X-Y difference, in the following cases.
258
259               align      condition for diffxy_minimum=0
260               ------     -----------------------------
261               centre              step <= 2
262               right               step <= 1
263               left                always
264

OEIS

266       Entries in Sloane's Online Encyclopedia of Integer Sequences related to
267       this path include
268
269           <http://oeis.org/A023531> (etc)
270
271           step=1
272             A002262    X coordinate, runs 0 to k
273             A003056    Y coordinate, k repeated k+1 times
274             A051162    X+Y sum
275             A025581    Y-X diff, runs k to 0
276             A079904    X*Y product
277             A069011    X^2+Y^2, n_to_rsquared()
278             A080099    X bitwise-AND Y
279             A080098    X bitwise-OR  Y
280             A051933    X bitwise-XOR Y
281             A050873    GCD(X+1,Y+1) greatest common divisor by rows
282             A051173    LCM(X+1,Y+1) least common multiple by rows
283
284             A023531    dY, being 1 at triangular numbers (but starting n=0)
285             A167407    dX-dY, change in X-Y (extra initial 0)
286             A129184    turn 1=left, 0=right or straight
287
288             A079824    N total along each opposite diagonal
289             A000124    N on Y axis (triangular+1)
290             A000217    N on X=Y diagonal, extra initial 0
291           step=1, n_start=0
292             A109004    GCD(X,Y) greatest common divisor starting (0,0)
293             A103451    turn 1=left or right,0=straight, but extra initial 1
294             A103452    turn 1=left,0=straight,-1=right, but extra initial 1
295
296           step=2
297             A196199    X coordinate, runs -n to +n
298             A000196    Y coordinate, n appears 2n+1 times
299             A053186    X+Y, being distance to next higher square
300             A010052    dY,  being 1 at perfect square row end
301             A000290    N on X=Y diagonal, extra initial 0
302             A002522    N on X=-Y North-West diagonal (start row), Y^2+1
303             A004201    N for which X>=0, ie. right hand half
304             A020703    permutation N at -X,Y
305           step=2, n_start=0
306             A005563    N on X=Y diagonal, Y*(Y+2)
307             A000290    N on X=-Y North-West diagonal (start row), Y^2
308           step=2, n_start=2
309             A059100    N on north-west diagonal (start each row), Y^2+2
310             A053615    abs(X), runs k..0..k
311           step=2, align=right, n_start=0
312             A196199    X-Y, runs -k to +k
313             A053615    abs(X-Y), runs k..0..k
314           step=2, align=left, n_start=0
315             A005563    N on Y axis, Y*(Y+2)
316
317           step=3
318             A180447    Y coordinate, n appears 3n+1 times
319             A104249    N on Y axis, Y*(3Y+1)/2+1
320             A143689    N on X=-Y North-West diagonal
321           step=3, n_start=0
322             A005449    N on Y axis, second pentagonals Y*(3Y+1)/2
323             A000326    N on diagonal north-west, pentagonals Y*(3Y-1)/2
324
325           step=4
326             A084849    N on Y axis
327             A001844    N on X=Y diagonal (North-East)
328             A058331    N on X=-Y North-West diagonal
329             A221217    permutation N at -X,Y
330           step=4, n_start=0
331             A014105    N on Y axis, the second hexagonal numbers
332             A046092    N on X=Y diagonal, 4*triangular numbers
333           step=4, align=right, n_start=0
334             A060511    X coordinate, amount n exceeds hexagonal number
335             A000384    N on Y axis, the hexagonal numbers
336             A001105    N on X=Y diagonal, 2*squares
337
338           step=5
339             A116668    N on Y axis
340
341           step=6
342             A056108    N on Y axis
343             A056109    N on X=Y diagonal (North-East)
344             A056107    N on X=-Y North-West diagonal
345
346           step=8
347             A053755    N on X=-Y North-West diagonal
348
349           step=9
350             A006137    N on Y axis
351             A038764    N on X=Y diagonal (North-East)
352

SEE ALSO

354       Math::PlanePath, Math::PlanePath::PyramidSides,
355       Math::PlanePath::Corner, Math::PlanePath::SacksSpiral,
356       Math::PlanePath::MultipleRings
357
358       Math::PlanePath::Diagonals, Math::PlanePath::DiagonalsOctant,
359       Math::PlanePath::Rows
360

HOME PAGE

362       <http://user42.tuxfamily.org/math-planepath/index.html>
363

LICENSE

365       Copyright 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018 Kevin
366       Ryde
367
368       This file is part of Math-PlanePath.
369
370       Math-PlanePath is free software; you can redistribute it and/or modify
371       it under the terms of the GNU General Public License as published by
372       the Free Software Foundation; either version 3, or (at your option) any
373       later version.
374
375       Math-PlanePath is distributed in the hope that it will be useful, but
376       WITHOUT ANY WARRANTY; without even the implied warranty of
377       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
378       General Public License for more details.
379
380       You should have received a copy of the GNU General Public License along
381       with Math-PlanePath.  If not, see <http://www.gnu.org/licenses/>.
382
383
384
385perl v5.30.0                      2019-08-17   Math::PlanePath::PyramidRows(3)
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