On Jun 3, 2009, at 5:29 PM, Andreas Grassl wrote:
Barry Smith schrieb:
When properly running nn-cg (are you sure everything is symmetric?) should require 10-30 iterations (certainly for model problems)
ok, this was the number I expected.
nn-cg on 2 nodes 229 iterations, condition 6285 nn-cg on 4 nodes 331 iterations, condition 13312
Are you sure that your operator has the null space of only constants?
no, I didn't touch anything regarding the null space since I thought it would be done inside the NN-preconditioner. Does this mean I have to set up a null space of the size of the Schur complement system, i.e. the number of interface DOF's?
No, I don't think you need to do anything about the null space. The code in PETSc for NN is for (and only for) a null space of constants. BTW: with 2 or 4 subdomains they all touch the boundary and likely don't have a null space anyways. Run with -ksp_view and make sure the local solves are being done with LU Barry
cheers,
ando
Barry
On Jun 3, 2009, at 5:29 AM, Andreas Grassl wrote:
Barry Smith schrieb:
Hmm, it sounds like the difference between local "ghosted" vectors and the global parallel vectors. But I do not understand why any of the local vector entries would be zero. Doesn't the vector X that is passed into KSP (or SNES) have the global entries and uniquely define the solution? Why is viewing that not right?
I still don't understand fully the underlying processes of the whole PCNN solution procedure, but trying around I substituted
MatCreateIS(commw, ind_length, ind_length, PETSC_DECIDE, PETSC_DECIDE, gridmapping, &A);
by
MatCreateIS(commw, PETSC_DECIDE, PETSC_DECIDE, actdof, actdof, gridmapping, &A);
and received the needed results.
Furthermore it seems, that the load balance is now better, although I still don't reach the expected values, e.g. ilu-cg 320 iterations, condition 4601 cg only 1662 iterations, condition 84919
nn-cg on 2 nodes 229 iterations, condition 6285 nn-cg on 4 nodes 331 iterations, condition 13312
or is it not to expect, that nn-cg is faster than ilu-cg?
cheers,
ando
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