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# Copyright 2012, 2013, 2014 Kevin Ryde
# This file is part of Math-PlanePath.
#
# Math-PlanePath 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.
#
# Math-PlanePath 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 Math-PlanePath. If not, see <http://www.gnu.org/licenses/>.
# A056520 1,2,6,15 (n+2)*(2*n^2-n+3)/6 starting n=0
#
package Math::PlanePath::ParabolicRows;
use 5.004;
use strict;
#use List::Util 'min', 'max';
*min = \&Math::PlanePath::_min;
use vars '$VERSION', '@ISA';
$VERSION = 117;
use Math::PlanePath;
@ISA = ('Math::PlanePath');
use Math::PlanePath::Base::Generic
'is_infinite',
'round_nearest';
# uncomment this to run the ### lines
#use Smart::Comments;
use constant class_x_negative => 0;
use constant class_y_negative => 0;
use constant n_frac_discontinuity => .5;
# first N in row, counting from N=1 at X=0,Y=0
# [ 0,1,2,3 ],
# [ 1,2,6,15 ]
# N = (1/3 y^3 + 1/2 y^2 + 1/6 y + 1)
# = (2 y^3 + 3 y^2 + y + 1) / 6
# = ((2*y + 3)*y + 1)*y/6 + 1 + $x;
sub n_to_xy {
my ($self, $n) = @_;
### ParabolicRows n_to_xy(): $n
if ($n < 1) { return; }
if (is_infinite($n)) { return ($n,$n); }
my $int = int($n);
$n -= $int;
if (2*$n >= 1) { # if frac>=0.5
$int += 1;
$n -= 1;
}
### $int
### $n
my $yhi = int(sqrt($int)) + 2;
my $y = 0;
for (;;) {
my $ymid = int(($yhi+$y)/2);
### at: "y=$y ymid=$ymid yhi=$yhi"
if ($ymid == $y) {
### assert: $y+1 == $yhi
### found, row starting: ((2*$y + 3)*$y + 1)*$y/6 + 1
### $y
### x: $n + ($int - ((2*$y + 3)*$y + 1)*$y/6)
return ($n + ($int - ((2*$y + 3)*$y + 1)*$y/6 - 1),
$y);
}
### compare: ((2*$ymid + 3)*$ymid + 1)*$ymid/6 + 1
if ($int >= ((2*$ymid + 3)*$ymid + 1)*$ymid/6 + 1) {
$y = $ymid;
} else {
$yhi = $ymid;
}
}
# my $y = 0;
# for (;;) {
# my $max = ($y+1)**2;
# if ($int <= $max) {
# return ($n+$int-1,$y);
# }
# $y++;
# $int -= $max;
# }
}
sub xy_to_n {
my ($self, $x, $y) = @_;
### ParabolicRows xy_to_n(): "$x, $y"
$x = round_nearest ($x);
$y = round_nearest ($y);
if ($y < 0) {
return undef;
}
my $ysquared = ($y+1)*($y+1);
if ($x >= $ysquared) {
return undef;
}
return ((2*$y + 3)*$y + 1)*$y/6 + 1 + $x;
}
# exact
sub rect_to_n_range {
my ($self, $x1,$y1, $x2,$y2) = @_;
### ParabolicRows rect_to_n_range(): "$x1,$y1 $x2,$y2"
$x1 = round_nearest ($x1);
$y1 = round_nearest ($y1);
$x2 = round_nearest ($x2);
$y2 = round_nearest ($y2);
($x1,$x2) = ($x2,$x1) if $x1 > $x2;
($y1,$y2) = ($y2,$y1) if $y1 > $y2;
if ($x2 < 0 || $y2 < 0) {
### all outside first quadrant ...
return (1, 0);
}
if ($y1 < 0) {
$y1 *= 0;
}
if ($x1 < 0) {
$x1 *= 0;
} elsif ($x1 >= ($y1+1)*($y1+1)) {
$y1 = _sqrt_ceil($x1+1);
### increase y1 to put x1 in range: $y1
}
### assert: defined $self->xy_to_n ($x1, $y1)
### assert: defined $self->xy_to_n (min($x2,($y2+2)*$y2), $y2)
# monotonic increasing in $x and $y directions, so this is exact
return ($self->xy_to_n ($x1, $y1),
$self->xy_to_n (min($x2,($y2+2)*$y2), $y2));
}
sub _sqrt_ceil {
my ($n) = @_;
my $sqrt = sqrt($n);
if ($sqrt*$sqrt < $n) {
$sqrt += 1;
}
return $sqrt;
}
1;
__END__
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