[Trilinos-Users] preconditioned GMRES: no convergence in explicit residual
Nico Schlömer
nico.schloemer at gmail.com
Fri Jan 31 10:58:38 MST 2014
Hi all,
I've got this matrix corresponding a finite-element discretization of
the Poisson problem on the unit square (with Dirichlet BC, no issues
here). Running the problem through Belos with CG and ML, Ifpack gives
no problems at all. The PseudoBlockGMRES solver works fine when
unpreconditioned, but yields something weird when using a
preconditioner:
============== *snip* ==============
*******************************************************
***** Belos Iterative Solver: Pseudo Block Gmres
***** Maximum Iterations: 100
***** Block Size: 1
***** Residual Tests (SEQ):
***** Test 1 : Belos::StatusTestGenResNorm<>: (2-Norm Imp Res Vec) /
(2-Norm Prec Res0), tol = 1e-13
***** Test 2 : Belos::StatusTestGenResNorm<>: (2-Norm Exp Res Vec) /
(2-Norm Res0), tol = 1e-13
*******************************************************
Iter 0, [ 1] : 1.000000e+00 ---
Iter 1, [ 1] : 6.120593e-01 ---
Iter 2, [ 1] : 2.695238e-01 ---
Iter 3, [ 1] : 5.704995e-02 ---
Iter 4, [ 1] : 1.272673e-02 ---
Iter 5, [ 1] : 2.783810e-03 ---
Iter 6, [ 1] : 5.753817e-04 ---
Iter 7, [ 1] : 2.045848e-04 ---
Iter 8, [ 1] : 5.724907e-05 ---
Iter 9, [ 1] : 1.633313e-05 ---
Iter 10, [ 1] : 3.055064e-06 ---
Iter 11, [ 1] : 4.947173e-07 ---
Iter 12, [ 1] : 6.945227e-08 ---
Iter 13, [ 1] : 1.859584e-08 ---
Iter 14, [ 1] : 5.185228e-09 ---
Iter 15, [ 1] : 5.922331e-10 ---
Iter 16, [ 1] : 8.149474e-11 ---
Iter 17, [ 1] : 1.010586e-11 ---
Iter 18, [ 1] : 1.600644e-12 ---
Iter 19, [ 1] : 3.034731e-13 ---
Iter 20, [ 1] : 3.452280e-14 7.213315e-01
[...]
============== *snap* ==============
The ExpResVec never converges at all.
What may cause this? Any known fix/workaround?
Cheers,
Nico
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