### What's wrong with the ILU sparse preconditioner?

Posted:

**Tue Jun 02, 2015 12:24 pm**Hi,

I have been trying to use the ILU preconditioner in sparse-iter. I'm using it for iterative linear solvers. I tried the testing_zsolver example for LAPLACE2D of size 200 with PBiCGSTAB (Jacobi and ILU preconditioners). The linear solve finishes in 0.2 seconds with Jacobi precond, and takes 300 seconds with ILU precond. Also, what's the difference between norm2 residual and exact residual?

# matrix info: 40000-by-40000 with 199598 nonzeros

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

% BiCGSTAB performance analysis every 100 iteration

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

% iter || residual-nrm2 || runtime

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

0 || 2.000000e+02 || 0.000000

100 || 3.552788e+01 || 0.057975

200 || 4.275729e-02 || 0.116186

300 || 4.799239e-08 || 0.174211

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

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

% PBiCGSTAB solver summary:

% initial residual: 2.000000e+02

% iterations: 371

% exact final residual: 2.415949e-09

% runtime: 0.2192 sec

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

---------------------------------------------------------------------------------------------------------------------------------------

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

% BiCGSTAB performance analysis every 100 iteration

% Preconditioner used: iterative ILU(0).

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

% iter || residual-nrm2 || runtime

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

0 || 2.000000e+02 || 0.000000

100 || 1.483437e-04 || 127.146813

200 || 2.915042e-11 || 254.295898

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

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

% PBiCGSTAB solver summary:

% initial residual: 2.000000e+02

% iterations: 233

% exact final residual: 1.990934e-09

% runtime: 296.2562 sec

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

Thanks,

Harshad

I have been trying to use the ILU preconditioner in sparse-iter. I'm using it for iterative linear solvers. I tried the testing_zsolver example for LAPLACE2D of size 200 with PBiCGSTAB (Jacobi and ILU preconditioners). The linear solve finishes in 0.2 seconds with Jacobi precond, and takes 300 seconds with ILU precond. Also, what's the difference between norm2 residual and exact residual?

# matrix info: 40000-by-40000 with 199598 nonzeros

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

% BiCGSTAB performance analysis every 100 iteration

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

% iter || residual-nrm2 || runtime

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

0 || 2.000000e+02 || 0.000000

100 || 3.552788e+01 || 0.057975

200 || 4.275729e-02 || 0.116186

300 || 4.799239e-08 || 0.174211

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

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

% PBiCGSTAB solver summary:

% initial residual: 2.000000e+02

% iterations: 371

% exact final residual: 2.415949e-09

% runtime: 0.2192 sec

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

---------------------------------------------------------------------------------------------------------------------------------------

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

% BiCGSTAB performance analysis every 100 iteration

% Preconditioner used: iterative ILU(0).

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

% iter || residual-nrm2 || runtime

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

0 || 2.000000e+02 || 0.000000

100 || 1.483437e-04 || 127.146813

200 || 2.915042e-11 || 254.295898

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

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

% PBiCGSTAB solver summary:

% initial residual: 2.000000e+02

% iterations: 233

% exact final residual: 1.990934e-09

% runtime: 296.2562 sec

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

Thanks,

Harshad