AlltoallvYkobi2d

#include <stdio.h>

#include <mpi.h>

#define WIDTH 5
#define HEIGHT 9
#define ITERS 1

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

    int proc_number = 0;            //номер процесса
    int proc_count = 0;         //кол. проц.
    MPI_Comm_rank(MPI_COMM_WORLD, &proc_number);
    MPI_Comm_size(MPI_COMM_WORLD, &proc_count);

    if (proc_count > WIDTH) {
        printf("Too many proccess for WIDTH of %d", WIDTH);
        MPI_Finalize();
        return 0;
    }

    int width = 0;
    int height = HEIGHT;
    width = WIDTH / proc_count;
    if (proc_number < WIDTH % proc_count) {
        width += 1;
    }
    width += 2;
    height += 2;

    //---

    double arr[width][height];
    double arrNew[width][height];

    int i, j;
    for (i = 0; i < width; i++) {
        for (j = 0; j < height; j++) {
            if ((proc_number == 0 && i == 0) || (j == 0) ||
                (proc_number == proc_count - 1 && i == width - 1) || (j == height - 1)) {
                arr[i][j] = 1;
            arrNew[i][j] = 1;
            } else {
                arr[i][j] = 0;
            arrNew[i][j] = 0;
            }
        }
    }

    //---

    int iter;
    for (iter = 0; iter < ITERS; iter++) {
        for (i = 1; i < width - 1; i++) {
            for (j = 1; j < height - 1; j++) {
                    arrNew[i][j] = arr[i][j - 1] + arr[i][j + 1];
                    arrNew[i][j] += arr[i - 1][j] + arr[i + 1][j];
                    arrNew[i][j] /= 4.0;
            }
        }


        //---
        int tt;
        int displs[proc_count];
         if (proc_number > 0) {
        int counts[proc_count];
        for (tt = 0; tt < proc_count; tt++) {
            counts[tt] = 0;
        }
        counts[proc_number - 1] = height - 2;
        for (tt = 0; tt < proc_count; tt++) {
        displs[tt] = 0;
        }

        MPI_Alltoallv(&arrNew[1][1], counts, displs, MPI_DOUBLE,
                         &arr[0][1], counts, displs, MPI_DOUBLE, MPI_COMM_WORLD);
         }

        if (proc_number < proc_count - 1) {
        int counts[proc_count];
        for (tt = 0; tt < proc_count; tt++) {
            counts[tt] = 0;
        }
        counts[proc_number + 1] = height - 2;
        int displs[proc_count];
        for (tt = 0; tt < proc_count; tt++) {
        displs[tt] = 0;
        }
        MPI_Alltoallv(&arrNew[width - 2][1], counts, displs, MPI_DOUBLE,
                         &arr[width - 1][1], counts, displs, MPI_DOUBLE, MPI_COMM_WORLD);
        }


        for (i = 1 ; i < width - 1; i++)
            for (j = 1 ; j < height - 1; j++)
                arr[i][j]=arrNew[i][j];

    }

    //---

    if (proc_number == 0) {
        fclose(fopen("output.txt", "w"));
    }

    int k;
    for (k = 0; k < proc_count; k++) {
        MPI_Barrier(MPI_COMM_WORLD);

        if (k == proc_number) {
            FILE* out = fopen("output.txt", "a");

            int start = 1;
            if (proc_number == 0) {
                start = 0;
            }
            int end = width - 1;
            if (proc_number == proc_count - 1) {
                end = width;
            }
            for (i = start; i < end; i++) {
                for (j = 0; j < height; j++) {
                    fprintf(out, "%lf ", arr[i][j]);
                }
                fprintf(out, "\n");
            }
            //fprintf(out, "\n---\n\n");

            fclose(out);
        }
    }

    MPI_Finalize();
    return 0;
}