.\" Automatically generated by Pod::Man 2.28 (Pod::Simple 3.29) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. Capital omega is used to do unbreakable dashes and .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, .\" nothing in troff, for use with C<>. .tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is turned on, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{ . if \nF \{ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" ======================================================================== .\" .IX Title "Math::PlanePath::KnightSpiral 3pm" .TH Math::PlanePath::KnightSpiral 3pm "2016-05-03" "perl v5.22.2" "User Contributed Perl Documentation" .\" For nroff, turn off justification. Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" Math::PlanePath::KnightSpiral \-\- integer points around a square, by chess knight moves .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 3 \& use Math::PlanePath::KnightSpiral; \& my $path = Math::PlanePath::KnightSpiral\->new; \& my ($x, $y) = $path\->n_to_xy (123); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" This path traverses the plane by an infinite \*(L"knight's tour\*(R" in the form of a square spiral. .PP .Vb 2 \& ... \& 21 4 9 14 19 2 \& \& 10 15 20 3 8 28 1 \& \& 5 22 1 18 13 <\- Y=0 \& \& 16 11 24 7 2 27 1 \& \& 23 6 17 12 25 2 \& \& 26 \& \& ^ \& \-2 \-1 X=0 1 2 3 .Ve .PP Each step is a chess knight's move 1 across and 2 along, or vice versa. The pattern makes 4 cycles on a 2\-wide path around a square before stepping outwards to do the same again to a now bigger square. The above sample shows the first 4\-cycle around the central 1, then stepping out at 26 and beginning to go around the outside of the 5x5 square. .PP An attractive traced out picture of the path can be seen at the following page (quarter way down under \*(L"Open Knight's Tour\*(R"), .Sp .RS 4 .RE .PP See math-image to draw the path lines too. .SH "FUNCTIONS" .IX Header "FUNCTIONS" See \*(L"\s-1FUNCTIONS\*(R"\s0 in Math::PlanePath for behaviour common to all path classes. .ie n .IP """$path = Math::PlanePath::KnightSpiral\->new ()""" 4 .el .IP "\f(CW$path = Math::PlanePath::KnightSpiral\->new ()\fR" 4 .IX Item "$path = Math::PlanePath::KnightSpiral->new ()" Create and return a new knight spiral object. .ie n .IP """($x,$y) = $path\->n_to_xy ($n)""" 4 .el .IP "\f(CW($x,$y) = $path\->n_to_xy ($n)\fR" 4 .IX Item "($x,$y) = $path->n_to_xy ($n)" Return the X,Y coordinates of point number \f(CW$n\fR on the path. .Sp For \f(CW\*(C`$n < 1\*(C'\fR the return is an empty list, it being considered the path starts at 1. .ie n .IP """$n = $path\->xy_to_n ($x,$y)""" 4 .el .IP "\f(CW$n = $path\->xy_to_n ($x,$y)\fR" 4 .IX Item "$n = $path->xy_to_n ($x,$y)" Return the point number for coordinates \f(CW\*(C`$x,$y\*(C'\fR. \f(CW$x\fR and \f(CW$y\fR are each rounded to the nearest integer, which has the effect of treating each N in the path as centred in a square of side 1, so the entire plane is covered. .SH "OEIS" .IX Header "OEIS" This Knight's tour is in Sloane's \s-1OEIS\s0 following the Knight spiral and giving the resulting X,Y location by the \f(CW\*(C`SquareSpiral\*(C'\fR numbering. There's eight forms for 4 rotations and spiralling the same or opposite directions. .Sp .RS 4 (etc) .RE .PP .Vb 9 \& permutations \& A068608 same knight and square spiral directions \& A068609 rotate 90 degrees \& A068610 rotate 180 degrees \& A068611 rotate 270 degrees \& A068612 rotate 180 degrees, spiral opp dir (X negate) \& A068613 rotate 270 degrees, spiral opp dir \& A068614 spiral opposite direction (Y negate) \& A068615 rotate 90 degrees, spiral opp dir (X,Y transpose) .Ve .PP See \fIexamples/knights\-oeis.pl\fR for a sample program printing the values of A068608. .SH "SEE ALSO" .IX Header "SEE ALSO" Math::PlanePath, Math::PlanePath::SquareSpiral .SH "HOME PAGE" .IX Header "HOME PAGE" .SH "LICENSE" .IX Header "LICENSE" Copyright 2010, 2011, 2012, 2013, 2014, 2015, 2016 Kevin Ryde .PP This file is part of Math-PlanePath. .PP Math-PlanePath is free software; you can redistribute it and/or modify it under the terms of the \s-1GNU\s0 General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. .PP Math-PlanePath is distributed in the hope that it will be useful, but \&\s-1WITHOUT ANY WARRANTY\s0; without even the implied warranty of \s-1MERCHANTABILITY\s0 or \s-1FITNESS FOR A PARTICULAR PURPOSE. \s0 See the \s-1GNU\s0 General Public License for more details. .PP You should have received a copy of the \s-1GNU\s0 General Public License along with Math-PlanePath. If not, see .