CODEWITHSUNDEEP
functionmpi
Tomasz Gutkowski
Tomasz Gutkowski

Reputation: 1418

MPI. Running mpi in function

I want to run some function using mpi from main but I don't know how it should be. It looks like:

#define MAXSIZE 100
int main (int argc, char **argv) {
  int i;
  float matrixA[MAXSIZE][MAXSIZE], matrixB[MAXSIZE][MAXSIZE], matrixC[MAXSIZE][MAXSIZE];
  for(i=0;i<10;i++){
    multiply(matrixA, matrixB, matrixC);
  }
}
void multiply(float matrixA[MAXSIZE][MAXSIZE], float matrixB[MAXSIZE][MAXSIZE], float matrixC[MAXSIZE][MAXSIZE]) {
  int rank; //process rank
  int size; //number of processes
  MPI_Init(&argc, &argv); //initialize MPI operations
  MPI_Comm_rank(MPI_COMM_WORLD, &rank); //get the rank
  MPI_Comm_size(MPI_COMM_WORLD, &size); //get number of processes

  ...someoperation...
  MPI_Finalize();
}

I know how to run basic MPI without using other functions but I need this construction.

Upvotes: 2

Views: 1287

Answers (2)

Srini
Srini

Reputation: 178

This might be helpful to you.In your program, there is a for loop for(i=0;i<10;i++) { multiply(matrixA, matrixB, matrixC); } I feel that you are trying to execute multiplication 10 times.You can give each multiplication to one process.So you can use the command, mpirun -np 10 executable.

Upvotes: 1

powerrox
powerrox

Reputation: 1342

In an application instance, MPI can be initialized at most once. So the code structure you provided will not work.

the correct structure for your program is as follows:

#define MAXSIZE 100
int main (int argc, char **argv) {
  int i;
  float matrixA[MAXSIZE][MAXSIZE], matrixB[MAXSIZE][MAXSIZE], matrixC[MAXSIZE][MAXSIZE];
  int rank; //process rank
  int size; //number of processes
  MPI_Init(&argc, &argv); //initialize MPI operations
  MPI_Comm_rank(MPI_COMM_WORLD, &rank); //get the rank
  MPI_Comm_size(MPI_COMM_WORLD, &size); //get number of processes
  for(i=0;i<10;i++){
    multiply(matrixA, matrixB, matrixC);
  }
  MPI_Finalize();
}
void multiply(float matrixA[MAXSIZE][MAXSIZE], float matrixB[MAXSIZE][MAXSIZE], float matrixC[MAXSIZE][MAXSIZE]) {    
  ...someoperation...
}

Upvotes: 8

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