2016-10-19 11:51 GMT-04:00 Hamed Babaei <hamedbabae...@gmail.com>: > I need to compute the determinant of system_matrix to check if its positive > or negative so that I know my system_matrix is positive definite or not. That's what I thought. You don't need to know the determinant to do that, you can check the sign of the eigenvalues. If all the eigenvalues are positive, the matrix is positive definite. You can either use a separate routine to compute the eigenvalues (see step-36 dealii.org/8.4.1/doxygen/deal.II/step_36.html) or you can get an estimate of the eigenvalues when you are using GMRES (see http://dealii.org/8.4.1/doxygen/deal.II/classSolverGMRES.html#a7b12c13beeb2d307f244e4dd48c06859)
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