Re: MatGetSubMatrix() and MatGetSubMatrices()

[Yujie <recrusader@xxxxxxxxx>]

Dear Barry:

That is, if one wants to generate different sub-matrices at different nodes of the cluster from the same matrix, only MatGetSubMatrices() is available?

If I use MatDistribute_MPIAIJ to convert a sequential matrix to parallel one, how to control which nodes of the cluster the submatrix of the parallel matrix is distributed into? For example, in a cluster, there are 10 nodes, I only want to use the specified 5 nodes for 
 distributing the matrix. thanks a lot.

Regards,
Yujie


 On 3/4/08, Barry Smith <bsmith@xxxxxxxxxxx> wrote:
>  On Mar 4, 2008, at 1:47 AM, Yujie wrote:
>
>  > Hi, everyone
>  >
>  > #include "petscmat.h"
>  > PetscErrorCode PETSCMAT_DLLEXPORT MatGetSubMatrix(Mat mat,IS
>  > isrow,IS iscol,PetscInt csize,MatReuse cll,Mat *newmat)
>   > #include "petscmat.h"
>  > PetscErrorCode PETSCMAT_DLLEXPORT MatGetSubMatrices(Mat mat,PetscInt
>  > n,const IS irow[],const IS icol[],MatReuse scall,Mat *submat[])
>  >
>  > To my knowledge, I can't get different matrices at different nodes
>   > by setting different isrows and iscol with MatGetSubMatrix().
>  > Because isrow  is rows current processor should obtain and the iscol
>  > argument must be the same on each processor.
>  > Furthermore, I can't get different parallel matrices at different
>   > nodes by setting different irow[] and icolp[] with
>  > MatGetSubMatrices() assuming I only want to get a matrix at each node.
>  > Because this function only gets different sequential matrices at
>  > different nodes. Is it right?
>   >
>
>     MatGetSubMatrices() gets one or more sequential matrix on each
>  process.
>     MatGetSubMatrix() gets ONE parallel matrix that lives on the same
>  communicator has the original matrix
>
>
>  > Another equestion is how to partition the matrix when calling
>   > MatConvert() to convert a sequential matrix to a parallel one?
>
>
>     MatConvert() is not for converting sequential matrix to parallel;
>  the communicator of a the new matrix from MatConvert()
>  is always the same as the old one.
>
>     In petsc-dev there is a utility for AIJ matrices that takes a
>  given sequential AIJ matrix and makes it parallel, called
>
>  /*
>      Distributes a SeqAIJ matrix across a set of processes. Code
>  stolen from
>       MatLoad_MPIAIJ(). Horrible lack of reuse. Should be a routine for
>  each matrix type.
>
>      Only for square matrices
>  */
>  PetscErrorCode MatDistribute_MPIAIJ(MPI_Comm comm,Mat gmat,PetscInt
>  m,MatReuse reuse,Mat *inmat)
>
>
>
>     Barry
>
>
>
>  >
>  >
>  > Thanks a lot.
>  >
>  > Regards,
>  > Yujie