sending blocks of 2D array in C using MPI

Question

How do you send blocks of 2-D array to different processors? Suppose the 2D array size is 400x400 an I want to send blocks of sizes 100X100 to different processors. The idea

Answer 1

I just found it easier to check it that way.

#include 
#include 
#include 
#include "mpi.h"

/*
 This is a version with integers, rather than char arrays, presented in this
 very good answer: http://stackoverflow.com/a/9271753/2411320
 It will initialize the 2D array, scatter it, increase every value by 1 and then gather it back.
*/

int malloc2D(int ***array, int n, int m) {
    int i;
    /* allocate the n*m contiguous items */
    int *p = malloc(n*m*sizeof(int));
    if (!p) return -1;

    /* allocate the row pointers into the memory */
    (*array) = malloc(n*sizeof(int*));
    if (!(*array)) {
       free(p);
       return -1;
    }

    /* set up the pointers into the contiguous memory */
    for (i=0; i

Output:

linux16:>mpicc -o main main.c
linux16:>mpiexec -n 4 main Global array is:
 1  2  3  4
 5  6  7  8
 9 10 11 12
13 14 15 16
Local process on rank 0 is:
| 1  2 |
| 5  6 |
Local process on rank 1 is:
| 3  4 |
| 7  8 |
Local process on rank 2 is:
| 9 10 |
|13 14 |
Local process on rank 3 is:
|11 12 |
|15 16 |
Processed grid:
 2  3  4  5
 6  7  8  9
10 11 12 13
14 15 16 17