Daniel@0: function b = positive_semidefinite(M)
Daniel@0: %
Daniel@0: % Return true iff v M v' >= 0 for any vector v.
Daniel@0: % We do this by checking that all the eigenvalues are non-negative.
Daniel@0: 
Daniel@0: E = eig(M);
Daniel@0: if length(find(E>=0)) == length(E)
Daniel@0:   b = 1;
Daniel@0: else
Daniel@0:   b = 0;
Daniel@0: end