[petsc-users] Tips on integrating MPI ksp petsc into my application?

[Junchao Zhang]

On Tue, Dec 7, 2021 at 9:06 PM Faraz Hussain via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Thanks, I took a look at ex10.c in ksp/tutorials . It seems to do as you
> wrote, "it efficiently gets the matrix from the file spread out over all
> the ranks.".
>
> However, in my application I only want rank 0 to read and assemble the
> matrix. I do not want other ranks trying to get the matrix data. The reason
> is the matrix is already in memory when my application is ready to call the
> petsc solver.

What is the data structure of your matrix in memory?


>
>
> So if I am running with multiple ranks, I don't want all ranks assembling
> the matrix.  This would require a total re-write of my application which is
> not possible . I realize this may sounds confusing. If so, I'll see if I
> can create an example that shows the issue.
>
>
>
>
>
> On Tuesday, December 7, 2021, 10:13:17 AM EST, Barry Smith <
> bsmith at petsc.dev> wrote:
>
>
>
>
>
>
>   If you use MatLoad() it never has the entire matrix on a single rank at
> the same time; it efficiently gets the matrix from the file spread out over
> all the ranks.
>
> > On Dec 6, 2021, at 11:04 PM, Faraz Hussain via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >
> > I am studying the examples but it seems all ranks read the full matrix.
> Is there an MPI example where only rank 0 reads the matrix?
> >
> > I don't want all ranks to read my input matrix and consume a lot of
> memory allocating data for the arrays.
> >
> > I have worked with Intel's cluster sparse solver and their documentation
> states:
> >
> > " Most of the input parameters must be set on the master MPI process
> only, and ignored on other processes. Other MPI processes get all required
> data from the master MPI process using the MPI communicator, comm. "
>
>
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