Description of permutation

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permutation

PURPOSE

constructor for the permutation class

SYNOPSIS

function p = permutation(n)

DESCRIPTION

 constructor for the permutation class
 p = permutation(n) --- create a new (identity) permutation on 1:n
 p = permutation(vec) --- create a new permutation based on the array vec
 (which should be a permutation of 1:n).

CROSS-REFERENCE INFORMATION

This function calls:

• length length(p) gives the size of the permutation
• size size(p) returns the number of elements permuted and the number of cycles.

This function is called by:

• inv inv(p) returns the inverse permutation of p
• mpower p^t is p multiplied by itself t times. May have t <= 0.
• mtimes p*q is the composition of p and q
• random random(p) --- return a random reordering of the elements of p

SOURCE CODE

0001 function p = permutation(n)
0002 % constructor for the permutation class
0003 % p = permutation(n) --- create a new (identity) permutation on 1:n
0004 % p = permutation(vec) --- create a new permutation based on the array vec
0005 % (which should be a permutation of 1:n).
0006 
0007 if nargin==0
0008     n = 1;
0009 end
0010 
0011 bad = 'Input invalid: must be a permutation of 1:n or a single integer';
0012 [r,c] = size(n);
0013 
0014 if (r>1) && (c>1)
0015     error(bad);
0016 end
0017 
0018 if (r==1) && (c==1)
0019     x = 1:n;
0020 else
0021     x = n;
0022 end
0023 
0024 
0025 x = x(:)';
0026 n = length(x);
0027 
0028 
0029 y = sort(x);
0030 if any(y ~= 1:n)
0031     error(bad);
0032 end
0033 
0034 p.array = x;
0035 p = class(p,'permutation');

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