VecView behaviour

[Barry Smith]

   When properly running nn-cg (are you sure everything is symmetric?)
should require 10-30 iterations (certainly for model problems)

> 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?

     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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