On Tue, Dec 7, 2021 at 9:06 PM Faraz Hussain via petsc-users < petsc-users@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 < > bsm...@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@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. " > >
