VecView behaviour

Andreas Grassl Andreas.Grassl at
Wed Jun 3 05:29:00 CDT 2009

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);


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?



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