Find_indexmatrix

 [m,indexmatrix] = Find_indexmatrix(n) 
 Find_indexmatrix:   Given a number of variables, creates a structure that
                     associates an index to every possible edge of a full structure (all related
                     variables) 
 INPUTS
 n: Number of variables
 OUTPUTS
 m: Number of variables
 indexmatrix: Matrix where entry i,j has the associated index of edge i,j.

 Last version 8/26/2008. Roberto Santana (roberto.santana@ehu.es)

0001 function[m,indexmatrix] = Find_indexmatrix(n)
0002 % [m,indexmatrix] = Find_indexmatrix(n)
0003 % Find_indexmatrix:   Given a number of variables, creates a structure that
0004 %                     associates an index to every possible edge of a full structure (all related
0005 %                     variables)
0006 % INPUTS
0007 % n: Number of variables
0008 % OUTPUTS
0009 % m: Number of variables
0010 % indexmatrix: Matrix where entry i,j has the associated index of edge i,j.
0011 %
0012 % Last version 8/26/2008. Roberto Santana (roberto.santana@ehu.es)
0013 
0014 
0015 m = n*(n+1)/2; % Number of possible edges
0016 
0017 indexmatrix = zeros(n,n);  % Matrix of indices for edges
0018 a= 1;
0019 for i=1:n-1  
0020  for j=i+1:n
0021   indexmatrix(i,j) = a;    % Each edge has an associated index
0022   indexmatrix(j,i) = a;
0023   a = a + 1;
0024  end
0025 end