### Exact final residual: -nan/ info= -202

Posted:

**Thu Aug 24, 2017 8:18 am**Hello all,

I am trying to get X for the AX=B type of problem. I have a large banded sparse matrix A of double precision numbers. I chose GMRES as a solver. The code works with a small matrix size, but when I compile my code with a size of 4624 * 4624, i get the error bellow ,i also included the code.

% iter || residual-nrm2 || runtime || SpMV-count || info

%=================================================================================%

1 nan 0.256593 31 -202

%=================================================================================%

%=================================================================================%

% PGMRES(30) solver summary:

% initial residual: 0.000000e+00

% preconditioner setup: 0.0877 sec

% iterations: 1

% SpMV-count: 31

% exact final residual: -nan

% runtime: 0.2566 sec

% preconditioner runtime: 0.2334 sec

%=================================================================================%

Any help will be greatly appreciated.

Thanks, Ham

I am trying to get X for the AX=B type of problem. I have a large banded sparse matrix A of double precision numbers. I chose GMRES as a solver. The code works with a small matrix size, but when I compile my code with a size of 4624 * 4624, i get the error bellow ,i also included the code.

% iter || residual-nrm2 || runtime || SpMV-count || info

%=================================================================================%

1 nan 0.256593 31 -202

%=================================================================================%

%=================================================================================%

% PGMRES(30) solver summary:

% initial residual: 0.000000e+00

% preconditioner setup: 0.0877 sec

% iterations: 1

% SpMV-count: 31

% exact final residual: -nan

% runtime: 0.2566 sec

% preconditioner runtime: 0.2334 sec

%=================================================================================%

Any help will be greatly appreciated.

Thanks, Ham