CODEWITHSUNDEEP
c++mpieigen
GoingMyWay
GoingMyWay

Reputation: 17468

How to send the data in an Eigen::MatrixXd with MPI

I want to use MPI to send matrces between machines. The following are my test code

#include <iostream>
#include <Eigen/Dense>
#include <mpi.h>
using std::cin;
using std::cout;
using std::endl;
using namespace Eigen;

int main(int argc, char ** argv)
{
    MatrixXd a = MatrixXd::Ones(3, 4);
    int myrank;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    MPI_Status status;
    if (0 == myrank)
    {
        MPI_Send(&a, 96, MPI_BYTE, 1, 99, MPI_COMM_WORLD);
    }
    else if (1 == myrank)
    {
        MPI_Recv(&a, 96, MPI_BYTE, 0, 99, MPI_COMM_WORLD, &status);
        cout << "RANK " << myrank << endl;
        cout << a << endl;
    }
    MPI_Finalize();
    return 0;
}

It compiled success without error, but when I launched it, it returned the following error.

$ MPI mpiexec -n 2 ./sendMatrixTest
RANK 1
[HPNotebook:11633] *** Process received signal ***
[HPNotebook:11633] Signal: Segmentation fault (11)
[HPNotebook:11633] Signal code: Address not mapped (1)
[HPNotebook:11633] Failing at address: 0xf4ba40
--------------------------------------------------------------------------
mpiexec noticed that process rank 1 with PID 11633 on node HPNotebook exited on signal 11 (Segmentation fault).
--------------------------------------------------------------------------

how should I fix it? Thank you!

Upvotes: 2

Views: 2801

Answers (1)

Jonathan Dursi
Jonathan Dursi

Reputation: 50927

As @Matt points out, there is more in a MatrixXd container than just the data. However, since here you know the size and type of the matrix, you can just get a pointer to the plain old data using the data() method, so that this works:

#include <iostream>
#include <Eigen/Dense>
#include <mpi.h>
using std::cin;
using std::cout;
using std::endl;
using namespace Eigen;

int main(int argc, char ** argv)
{
    MatrixXd a = MatrixXd::Ones(3, 4);
    int myrank;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    MPI_Status status;
    if (0 == myrank)
    {
        MPI_Send(a.data(), 12, MPI_DOUBLE, 1, 99, MPI_COMM_WORLD);
    }
    else if (1 == myrank)
    {
        MPI_Recv(a.data(), 12, MPI_DOUBLE, 0, 99, MPI_COMM_WORLD, &status);
        cout << "RANK " << myrank << endl;
        cout << a << endl;
    }
    MPI_Finalize();
    return 0;
}

Upvotes: 9

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