gistfile1.cpp

#include "mpi.h"
#include <stdio.h>

int main(int argc, char *argv[]) {
    
    int numprocs, myid;
    int rows;
    int pagesPerProcessor;
    int begin;
    int pageCount;
    int k, m;
    double dampingFactor;
    double* xLocal;
    double* xGlobal;
    double* aMatrix;
    double* totalMatrix;

    // Init MPI
    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);

    // Proc 0 init stuff
    if (myid == 0) {
        rows = 100;
        dampingFactor = 0.15;
        pagesPerProcessor = rows / numprocs;
    }

    // Broadcast initial data
    MPI_Bcast(&dampingFactor, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);
    MPI_Bcast(&pagesPerProcessor, 1, MPI_INT, 0, MPI_COMM_WORLD);

    pageCount = pagesPerProcessor * numprocs;
    xLocal = new double[pagesPerProcessor];
    xGlobal = new double[pageCount];
    aMatrix = new double[pagesPerProcessor * pageCount];
    
    if (myid == 0) {
        totalMatrix = new double[pageCount * pageCount];
    }
    
    // Populate xLocal
    for (k = 0; k < pagesPerProcessor; k++) {
        xLocal[k] = 1.0f / (pageCount);
    }
    
    // Populate aMatrix
    // aMatrix[NodeFrom][NodeTo]
    begin = pagesPerProcessor * myid;
    
    // Add links to next pages
    for (k = 0; k < pagesPerProcessor - 1; k++) {
        aMatrix[(k * pageCount) + (begin + k + 1)] = 0.5f;
    }
    
    // Add links to previous pages
    for (k = 1; k < pagesPerProcessor - 1; k++) {
        aMatrix[(k * pageCount) + (begin + (k - 1))] = 0.5f;
    }
    
    // Set last node correctly
    aMatrix[((pagesPerProcessor - 1) * pageCount) + (begin + pagesPerProcessor - 2)] = 1.0f;
    
    // Set first node correctly
    if (myid == 0) {
        aMatrix[1] = 1.0f;
    } else {
        aMatrix[0] = 0.5f;
    }
    
    MPI_Gather(aMatrix, pagesPerProcessor * pageCount, MPI_DOUBLE,
        totalMatrix, pageCount * pageCount, MPI_DOUBLE,
        0, MPI_COMM_WORLD);
    
    if (myid == 0) {
        for (k = 0; k < pageCount; k++) {
            for (m = 0; m < pageCount; m++) {
                printf("%1.1f ", totalMatrix[(m * pageCount) + k]);
            }
            printf("\n");
        }
        
        // Clean up memory
        delete [] totalMatrix;
    }
    
    // Clean up memory
    delete [] aMatrix;
    delete [] xLocal;
    delete [] xGlobal;
    
    MPI_Finalize();
    
    return 0;
}