Question

I am trying to compile a code in C++ using code from : https://stackoverflow.com/questions/5953979/sending-and-receiving-array-using-mpi-part-2.

I use the following command to compile: mpiicpc -o <filename> xxxx.cc -lmpi

After I compile, all my errors seem to refer to the two functions i have defined in my source code to print output values and do the MPI Isend and MPI Irecv. Specifically, I get two types of errors

1. Error: Identifier “variable” is undefined
2. Error: Too few arguments in function call: MPI_Isend/MPI_Irecv and MPI Waitall();
   Finally, it exists with this message: compilation aborted for xxxx.cc (code 2).

Could you please point to what I must be doing wrong while defining the variables?

Here is an excerpt of my source code (The code in its entirety is available at https://stackoverflow.com/questions/5953979/sending-and-receiving-array-using-mpi-part-2):

int main (int argc, char *argv[])
{
int my_rank;
int p;
int source; 
int dest;
int tag = 0;

//Allocating Memory
double *A = new double[Rows*sizeof(double)];
double *B = new double[Rows*sizeof(double)];
....
....
....

//MPI Commands
MPI_Status status;
MPI_Init (&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
MPI_Comm_size(MPI_COMM_WORLD, &p);

//For number of beats

for (ibeat=0;ibeat<beats;ibeat++)
{
    for (i=0; i<Cols/2; i++)
    {
        for (y=0; y<Rows/2; y++)
        {
            if (my_rank == 0)
                if (i < 48)
                    if (y<48)
                       V[i][y] = 0;

            if (my_rank ==
              .....
                ....
                  ....        
        }
    }

    //Load the Array with the edge values
    for (r=0; r<Rows/2; y++)
    {
        if ((my_rank == 0) || (my_rank == 1))
        {
            A[r] = V[r][48];
            BB[r] = V[r][48];
        }

        if ((my_rank
            ...
            ...
    }

    prttofile ();
    outputpass ();
    ibeat = ibeat+1;
 }

 MPI_Finalize ();
}


void prttofile ()
{
for (i = 0; i<Cols/2; i++)
  {
    for (y = 0; y<Rows/2; y++)
    {
        if (my_rank == 0)
           fout << V[i][y] << " " ;
        ....
           .... 
    }
  }

if (my_rank == 0)
    fout << endl;
 ....
}


void outputpass ()
{
int test = 2;
if ((my_rank%test) == 0)
{
    MPI_Isend(C, Rows, MPI_DOUBLE, my_rank+1, MPI_COMM_WORLD); //Non blocking Send
    MPI_Irecv(CC, Rows, MPI_DOUBLE, my_rank+1, MPI_COMM_WORLD, &status); //Non Blocking Recv
}
else if ((my_rank%test) == 1)
....
....

MPI_Waitall ();
}

Answer 1

MPI_Isend() requires a lot more arguments than what you’ve supplied. Here’s your line:

MPI_Isend(C, Rows, MPI_DOUBLE, my_rank+1, MPI_COMM_WORLD);

Where’s the tag? Where’s the request?

Similarly, your MPI_Waitall() doesn’t have any arguments at all! You need the array of requests, the number of requests, and an array of statuses.

I suggest you read an example of non-blocking communication in MPI.