MatCreateMPIAIJ

[Matthew Knepley]

On 10/4/06, Xiaoxu Wang <xiwang at dragon.rutgers.edu> wrote:
>
> Does it work as long as the global length is several times of the local
> length?


I think you are misunderstanding these terms. The local length is the
number of matrix rows assigned to the given process. The global length
is the sum of the local lengths.

   Matt

Thanks
> Xiaoxu
>
> Matthew Knepley wrote:
>
> > On 10/4/06, *Xiaoxu Wang* <xiwang at dragon.rutgers.edu
> > <mailto:xiwang at dragon.rutgers.edu>> wrote:
> >
> >     Hi, Thank you for your help already. Can anybody tell me how to
> >     set the
> >     size of local matrix? Can I set it arbitrarily?
> >
> >
> > Yes, you can. If you also set the global size it must be consistent.
> >
> >    Matt
> >
> >     Xiaoxu
> >
> >     Xiaoxu Wang wrote:
> >
> >     >
> >     > The error is at line 1023 of " plog.c".
> >     > ---------------
> >     > An unhandled exception of type 'System.NullReferenceException'
> >     > occurred in Unknown Module.
> >     >
> >     > Additional information: Object reference not set to an instance
> >     of an
> >     > object.
> >     > ----------------
> >     >
> >     > The matrix I am trying to initialize is the stiffness matrix K of
> >     > finite element methods. Later the dynamical system is solved
> >     as  (I +
> >     > Dt*K) U(t+1) = U(t) + Dt.F(t) by calling KSPSolve. Any idea how
> >     to set
> >     > the number of local rows?  I am running the code on PC now, but
> want
> >     > to keep MatCreateMPIAIJ in it.
> >     > Xiaoxu
> >     > ----- Original Message ----- From: "Barry Smith" <
> >     bsmith at mcs.anl.gov <mailto:bsmith at mcs.anl.gov>>
> >     > To: <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>>
> >     > Sent: Tuesday, October 03, 2006 8:32 AM
> >     > Subject: Re: MatCreateMPIAIJ
> >     >
> >     >
> >     >>
> >     >>
> >     >> On Mon, 2 Oct 2006, Xiaoxu Wang wrote:
> >     >>
> >     >>> Hi,
> >     >>>
> >     >>>      I am a beginner on PETSC. This is my question about
> >     >>> MatCreateMPIAIJ. I
> >     >>> have a sparse matrix and only know the total number of
> >     nonzeros each
> >     >>> row. The
> >     >>> number of local rows and the number of local columns has been
> >     set to
> >     >>> PETSC_DECIDE. Therefore I don't know the size of each portion
> >     and it
> >     >>> is hard
> >     >>> to tell d_nnz and o_nnz. I use the total number of nunzeros as
> >     d_nnz
> >     >>> and get
> >     >>> an allocation error.
> >     >>
> >     >>
> >     >>
> >     >>   It would be helpful to know the exact error message:
> >     >>
> >     >>>  How to deal  with  this problem?  Should  I  explicitly
> >     >>> specify the number of local rows and the number of local
> >     columns and
> >     >>> calculate
> >     >>> d_nnz and o_nnz? Or let PETSC decide the number of local rows
> and
> >     >>> the number
> >     >>> of local columns, and  then use another function to get these
> >     >>> values? Any
> >     >>> other better solution?
> >     >>
> >     >>
> >     >>
> >     >>   You should specifically set the number of local rows and
> columns
> >     >> and then
> >     >> compute the values of d_nnz and o_nnz. How you determine d_nnz
> and
> >     >> o_nnz is
> >     >> problem dependent and depends on what type of discretization
> >     you are
> >     >> using:
> >     >> finite differences, elements etc.
> >     >>
> >     >>
> >     >>   Barry
> >     >>
> >     >>>
> >     >>> Thanks a lot,
> >     >>> Xiaoxu
> >     >>>
> >     >>>
> >     >>
> >     >>
> >     >
> >
> >
> >
> >
> > --
> > "Failure has a thousand explanations. Success doesn't need one" -- Sir
> > Alec Guiness
>
>
>


-- 
"Failure has a thousand explanations. Success doesn't need one" -- Sir Alec
Guiness
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