[petsc-users] Finding determinant and inverse matrix

[Немања Илић (Nemanja Ilic)]

On Friday 06 August 2010 12:55:19 Немања Илић (Nemanja Ilic) wrote:
> Hello,
> 
> For the matrix:		 2  -2  0
> 				-1   5  1
> 				 3   4  5
> I get determinant = 0.0384615. The correct answer is 26.
> Maybe I am doing LU Factorization wrong?
> This is how I do LU Factoring:
> 	ierr = MatGetOrdering(Ap,  MATORDERING_1WD,  &perm,  &iperm); CHKERRQ(ierr);
> 	ierr = MatFactorInfoInitialize(&info); CHKERRQ(ierr);
> 	ierr = MatLUFactor(Ap, perm, iperm, &info); CHKERRQ(ierr);
> 
> This is the correct LU upper factotrization:  3.000  4.000  5.000
> 								 0.000  6.333  2.667
> 								 0.000  0.000 -1.368
> This is what I get:	row 0: (0, 0.5)  (1, -2)  (2, 0)
> 				row 1: (0, -0.5)  (1, 0.25)  (2, 1)
> 				row 2: (0, 1.5)  (1, 1.75)  (2, 0.307692)
> 
> Thank you,
> regards,
> Nemanja
> 
> 
> On Wednesday 04 August 2010 23:19:37 you wrote:
> > On Wed, Aug 4, 2010 at 12:18 PM, Немања Илић (Nemanja Ilic) <
> > nemanja.ilic.81 at gmail.com> wrote:
> > 
> > > Hello,
> > >
> > > Thank you for you previous help. I wrote the code for calculating matrix
> > > determinant and inverse matrix and they don't break anymore. Still I have
> > > problems. I try to find determinant in the following way: First get LU
> > > factor of a matrix and then multiply it's diagonal elements. I don't get
> > > correct results. Could you tell me wheather the problem
> > 
> > 
> > That description does not help. What do you get? What is the correct answer?
> > Did you try it on a small
> > problem that you can factor by hand?
> > 
> > 
> > > is maybe in info structure? What information do you need to be able to help
> > > me? I find the inverse matrix in the following way: I create linear problem
> > > A * X = B where A is the input matrix, X is the inverse matrix, and B is
> > > identity matrix. I solve it using MatMatSolve. Could you possibly help me
> > > and what info do you need?
> > >
> > 
> > That should work.
> > 
> >    Matt
> > 
> > 
> > > Thank you in advance,
> > > Best regards,
> > > Nemanja
> > >
> > 
> > 
> > 
> 
> 
>