File: is_sym.m

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function sym = is_sym (A)
% sym = is_sym(A)
% 1 if A is square and upper tri., -1 if square and lower tri., 0 otherwise
%
% Example:
%   sym = is_sym (A) ;
% See also: cs_demo

%   Copyright 2006-2007, Timothy A. Davis.
%   http://www.cise.ufl.edu/research/sparse

[m n] = size (A) ;
sym = 0 ;
if (m == n)
    is_upper = nnz (tril (A,-1)) == 0 ;
    is_lower = nnz (triu (A,1)) == 0 ;
    if (is_upper)
        sym = 1 ;
    elseif (is_lower)
        sym = -1 ;
    end
end