c - Petsc - 将分布式 vector 合并为局部 vector

Question

我正在使用Petsc，我想组合一个分布式Vec，以便每个进程都有一个完整的Vec副本。我有一个最小的示例，它从一个数据数组开始，从中构造一个 MPI Vec，然后尝试使用 VecScatter 来组合来自多个进程的 vector 。当我这样做时，本地 vector 仅接收存储在第 0 个进程上的值，它不接收来自其他进程的信息。如何组合分布式 vector 来生成完整的局部 vector ？

#include <petscvec.h>

double primes[] = {2,3,5,7,11,13,17};
int nprimes = 7;

int main(int argc,char **argv)
{
    PetscInitialize(&argc,&argv, NULL,NULL);

    MPI_Comm       comm=MPI_COMM_WORLD;
    Vec xpar,xseq;
    PetscInt low,high;
    IS index_set_global, index_set_local;
    const PetscInt *indices;
    VecScatter vc;
    PetscErrorCode ierr;

    //Set up parallel vector
    ierr = VecCreateMPI(comm, PETSC_DETERMINE, nprimes, &xpar); CHKERRQ(ierr);
    ierr = VecGetOwnershipRange(xpar, &low, &high); CHKERRQ(ierr);
    ierr = ISCreateStride(comm, high - low, low, 1, &index_set_global); CHKERRQ(ierr);
    ierr = ISGetIndices(index_set_global, &indices); CHKERRQ(ierr);
    ierr = ISView(index_set_global, PETSC_VIEWER_STDOUT_WORLD); CHKERRQ(ierr);
    ierr = VecSetValues(xpar, high - low, indices, primes + low, INSERT_VALUES);CHKERRQ(ierr);
    ierr = VecAssemblyBegin(xpar); CHKERRQ(ierr);
    ierr = VecAssemblyEnd(xpar); CHKERRQ(ierr);
    ierr = VecView(xpar, PETSC_VIEWER_STDOUT_WORLD); CHKERRQ(ierr);

    //Scatter parallel vector so all processes have full vector
    ierr = VecCreateSeq(PETSC_COMM_SELF, nprimes, &xseq); CHKERRQ(ierr);
    //ierr = VecCreateMPI(comm, high - low, nprimes, &xseq); CHKERRQ(ierr);
    ierr = ISCreateStride(comm, high - low, 0, 1, &index_set_local); CHKERRQ(ierr);
    ierr = VecScatterCreate(xpar, index_set_local, xseq, index_set_global, &vc); CHKERRQ(ierr);
    ierr = VecScatterBegin(vc, xpar, xseq, ADD_VALUES, SCATTER_FORWARD); CHKERRQ(ierr);
    ierr = VecScatterEnd(vc, xpar, xseq, ADD_VALUES, SCATTER_FORWARD); CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_SELF, "\nPrinting out scattered vector\n"); CHKERRQ(ierr);
    ierr = VecView(xseq, PETSC_VIEWER_STDOUT_WORLD); CHKERRQ(ierr);

    PetscFinalize();
}

输出:

mpiexec -n 2 ./test

IS Object: 2 MPI processes
type: stride
[0] Index set is permutation
[0] Number of indices in (stride) set 4
[0] 0 0
[0] 1 1
[0] 2 2
[0] 3 3
[1] Number of indices in (stride) set 3
[1] 0 4
[1] 1 5
[1] 2 6
Vec Object: 2 MPI processes
type: mpi
Process [0]
2.
3.
5.
7.
Process [1]
11.
13.
17.

Printing out scattered vector

Printing out scattered vector
Vec Object: 1 MPI processes
type: seq
2.
3.
5.
7.
0.
0.
0.

Answer 1

VecScatterCreateToAll()正是您所需要的:

Creates a vector and a scatter context that copies all vector values to each processor

它用于 ksp/.../ex49.c 。最后，它是在vecmpitoseq.c中实现的.

命名约定可能受到 MPI 函数的启发，例如 MPI_Allgather() ，它将收集的数据分发到所有进程，同时 MPI_Gather()仅收集指定根进程的数据。