Question

This assignment requires me to develop a MPI program for the parallel Odd-Even sort and brings together three functions:

1. MPI_Compare_exchange() for the P2P compare and exchange operation
2. MPI_Sort() for the parallel odd-even sort operation
3. MPI_Is_sorted() test if the parallel array sort is done

I get these errors when compiling

OddEvenSort.c:102: error: invalid operands to binary / (have ‘int *’ and ‘int’)
OddEvenSort.c:102: error: subscripted value is neither array nor pointer
OddEvenSort.c:104: error: subscripted value is neither array nor pointer
OddEvenSort.c:112: error: subscripted value is neither array nor pointer
OddEvenSort.c:116: error: subscripted value is neither array nor pointer
OddEvenSort.c:123: error: subscripted value is neither array nor pointer

This is the code:

int MPI_Sort(int n,double * array, int root, MPI_Comm comm){

    int rank, x, m, size, a, i;
    if( rank == 0 )
    {
        array = (double *) calloc( n, sizeof(double) );
        srand( ((unsigned)time(NULL)+rank) );
        for( x = 0; x < n; x++ ) array[x]=((double)rand()/RAND_MAX)*m;
    }

    MPI_Scatter(array, n/size, MPI_DOUBLE, &a[0], n/size, MPI_DOUBLE, 0, comm );

    merge_sort(n/size,&a[0]);

    for(i=0;i<size;i++){

        if( (i+rank)%2 ==0 ){

            if( rank < size-1 ) 

                exchange(n/size,&a[0],rank,rank+1,comm);

            } else{

                if( rank > 0 ) exchange(n/size,&a[0],rank-1,rank,comm);

            }

            MPI_Barrier(comm);
        }

    MPI_Gather(&a[0], n/size, MPI_DOUBLE, array, n/size, MPI_DOUBLE, 0, comm);

    if( rank == 0 )
    {
        for( x = 0; x < n; x++ )  printf( "Output : %f\n", array[x] );

    }


}

I think it’s referring to this: &a[0] but I don’t know how to fix it. Any ideas?

Answer 1

‘a’ is defined as an int, not an array, so you can’t pass the address of element 0.

I think what you intended was that ‘a’ is defined as a double, and of the same size as ‘array’.

i.e

double a[n];