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

Open discussion for MAGMA library (Matrix Algebra on GPU and Multicore Architectures)
hsahasra
Posts: 32
Joined: Mon Jun 24, 2013 3:40 pm

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

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,

hartwig anzt
Posts: 90
Joined: Tue Sep 02, 2014 5:44 pm