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annotate toolboxes/FullBNT-1.0.7/KPMtools/nchoose2.m @ 0:e9a9cd732c1e tip

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first hg version after svn
author wolffd
date Tue, 10 Feb 2015 15:05:51 +0000
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wolffd@0 1 function c = nchoose2(v, f)
wolffd@0 2 %NCHOOSE2 All combinations of N elements taken two at a time.
wolffd@0 3 %
wolffd@0 4 % NCHOOSE2(1:N) or NCHOOSEK(V) where V is a vector of length N,
wolffd@0 5 % produces a matrix with N*(N-1)/2 rows and K columns. Each row of
wolffd@0 6 % the result has K of the elements in the vector V.
wolffd@0 7 %
wolffd@0 8 % NCHOOSE2(N,FLAG) is the same as NCHOOSE2(1:N) but faster.
wolffd@0 9 %
wolffd@0 10 % NCHOOSE2(V) is much faster than NCHOOSEK(V,2).
wolffd@0 11 %
wolffd@0 12 % See also NCHOOSEK, PERMS.
wolffd@0 13
wolffd@0 14 % Author: Peter J. Acklam
wolffd@0 15 % Time-stamp: 2000-03-03 13:03:59
wolffd@0 16 % E-mail: jacklam@math.uio.no
wolffd@0 17 % URL: http://www.math.uio.no/~jacklam
wolffd@0 18
wolffd@0 19 nargs = nargin;
wolffd@0 20 if nargs < 1
wolffd@0 21 error('Not enough input arguments.');
wolffd@0 22 elseif nargs == 1
wolffd@0 23 v = v(:);
wolffd@0 24 n = length(v);
wolffd@0 25 elseif nargs == 2
wolffd@0 26 n = v;
wolffd@0 27 else
wolffd@0 28 error('Too many input arguments.');
wolffd@0 29 end
wolffd@0 30
wolffd@0 31 [ c(:,2), c(:,1) ] = find( tril( ones(n), -1 ) );
wolffd@0 32
wolffd@0 33 if nargs == 1
wolffd@0 34 c = v(c);
wolffd@0 35 end