[petsc-users] MatGetRow for global rows of a parallel matrix
Matthew Knepley
knepley at gmail.com
Wed Jun 10 11:36:01 CDT 2020
On Wed, Jun 10, 2020 at 12:26 PM Eda Oktay <eda.oktay at metu.edu.tr> wrote:
> Matthew Knepley <knepley at gmail.com>, 10 Haz 2020 Çar, 19:13 tarihinde
> şunu yazdı:
> >
> > On Wed, Jun 10, 2020 at 12:07 PM Eda Oktay <eda.oktay at metu.edu.tr>
> wrote:
> >>
> >> Der Matt,
> >>
> >> When I looked at the results, I found that there are some problems I
> >> couldn't understand.
> >>
> >> First of all, I am working on a 72*4 matrix and as I said before, I
> >> want to have 72 different vectors having size 4 each, whose elements
> >> consist of the elements in the same row. And of course, all vectors
> >> should be in all processors (currently I am using 4 processors).
> >>
> >> When I use your scatter code, the output vector is divided into 4
> >> parts for 4 processors and each vector consists of 18 row vectors
> >> whose elements are arranged in a way that if I want to find zeroth row
> >> vector, its elements are located in 0th,18th,36th,54th elements.
> >
> >
> > Was the global size of the vector you wrapped around the dense matrix
> 72*4?
>
> Yes it is. I set up its global size to 72*4.
>
> >
> > If you use CreateToAll(), it will make a vector on each process which
> has the global size of the original vector.
>
> Although I set 72*4, the size of the vectors in each process is 72.
>
You can understand how it is hard to accept, as this code is tested every
night. Can you VecView() the input vector
to CreateToAll and the output vector, and send that output?
Thanks,
Matt
> Thanks,
>
> Eda
>
> >
> > Thanks,
> >
> > Matt
> >
> >>
> >> So, isn't scatter's goal is to scatter all values to all processors?
> >>
> >> Furthermore, I am trying to use my vectors in that way but isn't there
> >> any possible way that I can reach my goal entirely?
> >>
> >> Thanks so much for your help,
> >>
> >> Eda
> >>
> >> Matthew Knepley <knepley at gmail.com>, 10 Haz 2020 Çar, 18:11 tarihinde
> >> şunu yazdı:
> >> >
> >> > On Wed, Jun 10, 2020 at 10:09 AM Eda Oktay <eda.oktay at metu.edu.tr>
> wrote:
> >> >>
> >> >> Dear Matt,
> >> >>
> >> >> I have one last question I believe. Up to creating a dense matrix I
> >> >> did what you've suggested. Thank you so much for that.
> >> >>
> >> >> I created a new dense matrix. Now, how should I wrap each vector in a
> >> >> MatDense again? I mean, what is wrapping vectors in a matrix? To put
> >> >> each of them again as rows?
> >> >
> >> >
> >> > I thought you need a dense matrix for something, since you started
> with one. If you
> >> > do not, just do VecGetArray() on the vector from CreateToAll and use
> the values.
> >> >
> >> > Thanks,
> >> >
> >> > Matt
> >> >
> >> >>
> >> >> Thanks!
> >> >>
> >> >> Eda
> >> >>
> >> >> Matthew Knepley <knepley at gmail.com>, 10 Haz 2020 Çar, 16:16
> tarihinde
> >> >> şunu yazdı:
> >> >> >
> >> >> > On Wed, Jun 10, 2020 at 9:08 AM Eda Oktay <eda.oktay at metu.edu.tr>
> wrote:
> >> >> >>
> >> >> >> Dear Matt,
> >> >> >>
> >> >> >> Matthew Knepley <knepley at gmail.com>, 10 Haz 2020 Çar, 16:03
> tarihinde
> >> >> >> şunu yazdı:
> >> >> >> >
> >> >> >> > On Wed, Jun 10, 2020 at 8:56 AM Eda Oktay <
> eda.oktay at metu.edu.tr> wrote:
> >> >> >> >>
> >> >> >> >> Hi all,
> >> >> >> >>
> >> >> >> >> I am trying to get all the rows of a parallel matrix as
> individual
> >> >> >> >> vectors. For instance, if I have 72*4 matrix, I want to get 72
> >> >> >> >> different vectors having size 4.
> >> >> >> >>
> >> >> >> >> As far as I understood, MatGetRow is only for local rows, so
> >> >> >> >> MatGetOwnershipRange is used, however, when I tried this one, I
> >> >> >> >> couldn't get the whole and desired row vectors.
> >> >> >> >>
> >> >> >> >> In MatGetRow explanation, it is written that I should use
> >> >> >> >> MatCreateSubMatrices first, then use MatGetRow. But I couldn't
> >> >> >> >> understand to which extent I should create submatrices. I just
> need to
> >> >> >> >> have all 72 rows as 72 different vectors each having 4
> elements.
> >> >> >> >
> >> >> >> >
> >> >> >> > 1) For sparse matrices, the storage is always divided by row,
> so that values can only be retrieved for local rows with MatGetRow()
> >> >> >> >
> >> >> >> > 2) Is this matrix sparse? It sounds like it is dense.
> >> >> >>
> >> >> >> Matrix is dense.
> >> >> >>
> >> >> >> >
> >> >> >> > 3) Are you asking to get all matrix values on all processes? If
> so, I think the easiest thing to do is first wrap a Vec around the
> >> >> >> > values, then use VecScatterToAll(), then wrap each one in a
> MatDense again.
> >> >> >>
> >> >> >> Yes, I want all row vectors on all processes. In a dense matrix,
> >> >> >> should I still wrap a Vec around the values? I know I should use
> >> >> >> scatter but I couldn't even wrap a Vec around them.
> >> >> >
> >> >> >
> >> >> > I would do
> >> >> >
> >> >> > MatGetSize(&N);
> >> >> > MatGetLocalSize(&m);
> >> >> >
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatDenseGetArray.html
> >> >> > <create vector of local size m*N>
> >> >> >
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecPlaceArray.html
> >> >> >
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecScatterCreateToAll.html
> >> >> > <do scatter>
> >> >> >
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecResetArray.html#VecResetArray
> >> >> >
> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateDense.html
> >> >> > <use it>
> >> >> > <destroy matrix>
> >> >> > <destroy vector from CreateToAll>
> >> >> >
> >> >> > Thanks,
> >> >> >
> >> >> > Matt
> >> >> >
> >> >> >>
> >> >> >> Thanks so much!
> >> >> >>
> >> >> >> Eda
> >> >> >>
> >> >> >> >
> >> >> >> > Thanks,
> >> >> >> >
> >> >> >> > Matt
> >> >> >> >
> >> >> >> >>
> >> >> >> >> Thanks!
> >> >> >> >>
> >> >> >> >> Eda
> >> >> >> >
> >> >> >> >
> >> >> >> >
> >> >> >> > --
> >> >> >> > What most experimenters take for granted before they begin
> their experiments is infinitely more interesting than any results to which
> their experiments lead.
> >> >> >> > -- Norbert Wiener
> >> >> >> >
> >> >> >> > https://www.cse.buffalo.edu/~knepley/
> >> >> >
> >> >> >
> >> >> >
> >> >> > --
> >> >> > What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> >> >> > -- Norbert Wiener
> >> >> >
> >> >> > https://www.cse.buffalo.edu/~knepley/
> >> >
> >> >
> >> >
> >> > --
> >> > What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> >> > -- Norbert Wiener
> >> >
> >> > https://www.cse.buffalo.edu/~knepley/
> >
> >
> >
> > --
> > What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> > -- Norbert Wiener
> >
> > https://www.cse.buffalo.edu/~knepley/
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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