Math::PlanePath::Diagonals -- points in diagonal stripes
use Math::PlanePath::Diagonals; my $path = Math::PlanePath::Diagonals->new; my ($x, $y) = $path->n_to_xy (123);
This path follows successive diagonals going from the Y axis down to the X axis.
6 | 22 5 | 16 23 4 | 11 17 24 3 | 7 12 18 ... 2 | 4 8 13 19 1 | 2 5 9 14 20 Y=0 | 1 3 6 10 15 21 +------------------------- X=0 1 2 3 4 5
N=1,3,6,10,etc on the X axis is the triangular numbers. N=1,2,4,7,11,etc on the Y axis is the triangular plus 1, the next point visited after the X axis.
Option direction => 'up'
reverses the order within each diagonal to count upward from the X axis.
direction => "up" 5 | 21 4 | 15 20 3 | 10 14 19 ... 2 | 6 9 13 18 24 1 | 3 5 8 12 17 23 Y=0 | 1 2 4 7 11 16 22 +----------------------------- X=0 1 2 3 4 5 6
This is merely a transpose changing X,Y to Y,X, but it's the same as in DiagonalsOctant
and can be handy to control the direction when combining Diagonals
with some other path or calculation.
The default is to number points starting N=1 as shown above. An optional n_start
can give a different start, in the same diagonals sequence. For example to start at 0,
n_start => 0, n_start=>0 direction=>"down" direction=>"up" 4 | 10 | 14 3 | 6 11 | 9 13 2 | 3 7 12 | 5 8 12 1 | 1 4 8 13 | 2 4 7 11 Y=0 | 0 2 5 9 14 | 0 1 3 6 10 +----------------- +----------------- X=0 1 2 3 4 X=0 1 2 3 4
N=0,1,3,6,10,etc on the Y axis of "down" or the X axis of "up" is the triangular numbers Y*(Y+1)/2.
Options x_start => $x
and y_start => $y
give a starting position for the diagonals. For example to start at X=1,Y=1
7 | 22 x_start => 1, 6 | 16 23 y_start => 1 5 | 11 17 24 4 | 7 12 18 ... 3 | 4 8 13 19 2 | 2 5 9 14 20 1 | 1 3 6 10 15 21 Y=0 | +------------------ X=0 1 2 3 4 5
The effect is merely to add a fixed offset to all X,Y values taken and returned, but it can be handy to have the path do that to step through non-negatives or similar.
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
$path = Math::PlanePath::Diagonals->new ()
$path = Math::PlanePath::Diagonals->new (direction => $str, n_start => $n, x_start => $x, y_start => $y)
Create and return a new path object. The direction
option (a string) can be
direction => "down" the default direction => "up" number upwards from the X axis
($x,$y) = $path->n_to_xy ($n)
Return the X,Y coordinates of point number $n
on the path.
For $n < 0.5
the return is an empty list, it being considered the path begins 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 $n
as a square of side 1, so the quadrant x>=-0.5, y>=-0.5 is entirely covered.
($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.
The sum d=X+Y numbers each diagonal from d=0 upwards, corresponding to the Y coordinate where the diagonal starts (or X if direction=up).
d=2 \ d=1 \ \ \ d=0 \ \ \ \ \
N is then given by
d = X+Y N = d*(d+1)/2 + X + Nstart
The d*(d+1)/2 shows how the triangular numbers fall on the Y axis when X=0 and Nstart=0. For the default Nstart=1 it's 1 more than the triangulars, as noted above.
d can be expanded out to the following quite symmetric form. This almost suggests something parabolic but is still the straight line diagonals.
X^2 + 3X + 2XY + Y + Y^2 N = ------------------------ + Nstart 2
The above formula N=d*(d+1)/2 can be solved for d as
d = floor( (sqrt(8*N+1) - 1)/2 ) # with n_start=0
For example N=12 is d=floor((sqrt(8*12+1)-1)/2)=4 as that N falls in the fifth diagonal. Then the offset from the Y axis NY=d*(d-1)/2 is the X position,
X = N - d*(d-1)/2 Y = d - X
In the code fractional N is handled by imagining each diagonal beginning 0.5 back from the Y axis. That's handled by adding 0.5 into the sqrt, which is +4 onto the 8*N.
d = floor( (sqrt(8*N+5) - 1)/2 ) # N>=-0.5
The X and Y formulas are unchanged, since N=d*(d-1)/2 is still the Y axis. But each diagonal d begins up to 0.5 before that and therefor X extends back to -0.5.
Within each row increasing X is increasing N, and in each column increasing Y is increasing N. So in a rectangle the lower left corner is the minimum N and the upper right is the maximum N.
| \ \ N max | \ ----------+ | | \ |\ | |\ \ | | \| \ \ | | +---------- | N min \ \ \ +-------------------------
Entries in Sloane's Online Encyclopedia of Integer Sequences related to this path include
http://oeis.org/A002262 (etc)
direction=down (the default) A002262 X coordinate, runs 0 to k A025581 Y coordinate, runs k to 0 A003056 X+Y coordinate sum, k repeated k+1 times A114327 Y-X coordinate diff A101080 HammingDist(X,Y) A127949 dY, change in Y coordinate A000124 N on Y axis, triangular numbers + 1 A001844 N on X=Y diagonal A185787 total N in row to X=Y diagonal A185788 total N in row to X=Y-1 A100182 total N in column to Y=X diagonal A101165 total N in column to Y=X-1 A185506 total N in rectangle 0,0 to X,Y direction=down, n_start=0 A023531 dSum = dX+dY, being 1 at N=triangular+1 (and 0) A000096 N on X axis, X*(X+3)/2 A000217 N on Y axis, the triangular numbers A129184 turn 1=left,0=right A103451 turn 1=left or right,0=straight, but extra initial 1 A103452 turn 1=left,0=straight,-1=right, but extra initial 1 direction=up, n_start=0 A129184 turn 0=left,1=right direction=up, n_start=-1 A023531 turn 1=left,0=right direction=down, n_start=-1 A023531 turn 0=left,1=right in direction=up the X,Y coordinate forms are the same but swap X,Y either direction, n_start=1 A038722 permutation N at transpose Y,X which is direction=down <-> direction=up n_start=1, x_start=1, y_start=1, either direction A003991 X*Y coordinate product A003989 GCD(X,Y) greatest common divisor starting (1,1) A003983 min(X,Y) A051125 max(X,Y) n_start=1, x_start=1, y_start=1, direction=down A057046 X for N=2^k A057047 Y for N=2^k n_start=0 (either direction) A049581 abs(X-Y) coordinate diff A004197 min(X,Y) A003984 max(X,Y) A004247 X*Y coordinate product A048147 X^2+Y^2 A109004 GCD(X,Y) greatest common divisor starting (0,0) A004198 X bit-and Y A003986 X bit-or Y A003987 X bit-xor Y A156319 turn 0=straight,1=left,2=right A061579 permutation N at transpose Y,X which is direction=down <-> direction=up
Math::PlanePath, Math::PlanePath::DiagonalsAlternating, Math::PlanePath::DiagonalsOctant, Math::PlanePath::Corner, Math::PlanePath::Rows, Math::PlanePath::Columns
http://user42.tuxfamily.org/math-planepath/index.html
Copyright 2010, 2011, 2012, 2013, 2014, 2015, 2016 Kevin Ryde
This file is part of Math-PlanePath.
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