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%%*******************************************************************
%% Create a column vector representing a symmetric matrix.
%%
%% V = DSPARSE(i,j,s,m,n) uses the same arguments as SPARSE(i,j,s,m,n)
%%
%% However, this routine assumes the matrix will be symmetric, so
%% that n must equal m. The rows of [i,j,s] to generate an
%% n-by-n sparse matrix with space allocated for length(s) nonzeros. The
%% two integer index vectors, i and j, and the real entries
%% vector, s, all have the same length, which is the number of
%% nonzeros in the resulting sparse matrix S . When duplicate values
%% for a matrix element are provided, that last one will be used.
%%
%% Output: V = column vector representing half of a symmetric matrix.
%% A matrix with n rows and columns, implies V is a column
%% vector with n*(n+1)/2 rows. This column vector is in
%% the format used by DSDP for symmetric data matrices.
%%
%% Given the nonzero elements (i,j,s) that are on or above the diagonal,
%% this routine could be defined as: V = dvec( sparse(i,j,s,n,n) );
%%
%% See also: DVEC
%%
%% DSDP5.6
%% Copyright (c) 2005 by
%% S. Benson and Y. Ye
%% Last modified: December 2005
%%******************************************************************
function [V]=dsparse(irow,jcol,nz,n1,n2);
if (n1~=n2) error('Matrix not square.'); end;
if (size(jcol,1)~=size(irow,1)) error('Number of Row indices do not equal the number of column indices.'); end;
if (size(jcol,2)~=size(irow,2)) error('Number of Row indices do not equal the number of column indices.'); end;
if (size(jcol,1)~=size(nz,1)) error('Number of Row indices do not equal the number of nonzeros.'); end;
if (size(jcol,2)~=size(nz,2)) error('Number of Row indices do not equal the number of nonzeros'); end;
nn=n1*(n1+1)/2;
nnz=length(nz);
V=sparse(nn,1);
idx=zeros(nnz,1);
%% idx=(irow .* irow - irow)/2 + jcol
for k=1:nnz,
ii=irow(k);
jj=jcol(k);
if (jj>ii) tt=ii;ii=jj;jj=tt; end;
kk=ii*(ii-1)/2+jj;
idx(k)=kk;
end;
V(idx)=nz;
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