multiply_no_comm

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

void Check_for_error(int local_ok, char fname[], char message[],
      MPI_Comm comm);
void Get_dims(int* m_p, int* local_m_p, int* n_p, int* local_n_p,
      int my_rank, int comm_sz, MPI_Comm comm);
void Allocate_arrays(double** local_A_pp, double** local_x_pp,
      double** local_y_pp, int local_m, int n, int local_n,
      MPI_Comm comm);
void Read_matrix(char prompt[], double local_A[], int m, int local_m,
      int n, int my_rank, MPI_Comm comm);
void Read_vector(char prompt[], double local_vec[], int n, int local_n,
      int my_rank, MPI_Comm comm);
void Print_matrix(char title[], double local_A[], int m, int local_m,
      int n, int my_rank, MPI_Comm comm);
void Print_vector(char title[], double local_vec[], int n,
      int local_n, int my_rank, MPI_Comm comm);
void Mat_vect_mult(double local_A[], double local_x[],
      double local_y[], int local_m, int n, int local_n,
      MPI_Comm comm);

/*-------------------------------------------------------------------*/
int main(void) {
   double* local_A;
   double* local_x; double* local_y;
   int my_rank, comm_sz, m, local_m, n, local_n;
   MPI_Comm comm;

   MPI_Init(NULL, NULL);
   comm = MPI_COMM_WORLD;
   MPI_Comm_size(comm, &comm_sz);
   MPI_Comm_rank(comm, &my_rank);

   Get_dims(&m, &local_m, &n, &local_n, my_rank, comm_sz, comm);
   Allocate_arrays(&local_A, &local_x, &local_y, local_m, n, local_n, comm);

   Read_matrix("A", local_A, m, local_m, n, my_rank, comm);
   Print_matrix("A", local_A, m, local_m, n, my_rank, comm);

   Read_vector("x", local_x, n, local_n, my_rank, comm);
   Print_vector("x", local_x, n, local_n, my_rank, comm);

   Mat_vect_mult(local_A, local_x, local_y, local_m, n, local_n, comm);
   Print_vector("y", local_y, m, local_m, my_rank, comm);

   free(local_A); free(local_x); free(local_y);

   MPI_Finalize();
   return 0;
}  /* main */

void Check_for_error(
      int       local_ok   /* in */,
      char      fname[]    /* in */,
      char      message[]  /* in */,
      MPI_Comm  comm       /* in */) {
   int ok;

   MPI_Allreduce(&local_ok, &ok, 1, MPI_INT, MPI_MIN, comm);
   if (ok == 0) {
      int my_rank;
      MPI_Comm_rank(comm, &my_rank);
      if (my_rank == 0) {
         fprintf(stderr, "Proc %d > In %s, %s\n", my_rank, fname,
               message);
         fflush(stderr);
      }
      MPI_Finalize();
      exit(-1);
   }
}  /* Check_for_error */

void Get_dims(
      int*      m_p        /* out */,
      int*      local_m_p  /* out */,
      int*      n_p        /* out */,
      int*      local_n_p  /* out */,
      int       my_rank    /* in  */,
      int       comm_sz    /* in  */,
      MPI_Comm  comm       /* in  */) {
   int local_ok = 1;

   if (my_rank == 0) {
      printf("Enter the number of rows\n");
      scanf("%d", m_p);
      printf("Enter the number of columns\n");
      scanf("%d", n_p);
   }
   MPI_Bcast(m_p, 1, MPI_INT, 0, comm);
   MPI_Bcast(n_p, 1, MPI_INT, 0, comm);
   if (*m_p <= 0 || *n_p <= 0 || *m_p % comm_sz != 0
         || *n_p % comm_sz != 0) local_ok = 0;
   Check_for_error(local_ok, "Get_dims",
      "m and n must be positive and evenly divisible by comm_sz",
      comm);

   *local_m_p = *m_p/comm_sz;
   *local_n_p = *n_p/comm_sz;
}  /* Get_dims */

void Allocate_arrays(
      double**  local_A_pp  /* out */,
      double**  local_x_pp  /* out */,
      double**  local_y_pp  /* out */,
      int       local_m     /* in  */,
      int       n           /* in  */,
      int       local_n     /* in  */,
      MPI_Comm  comm        /* in  */) {
   int local_ok = 1;

   *local_x_pp = malloc(local_n * sizeof(double));
   *local_y_pp = malloc(local_m * sizeof(double));
   *local_A_pp = malloc(local_m * n * sizeof(double));

   if (*local_A_pp == NULL || local_x_pp == NULL || local_y_pp == NULL)
      local_ok = 0;
   Check_for_error(local_ok, "Allocate_arrays",
         "Can't allocate local arrays", comm);
}  /* Allocate_arrays */

void Read_matrix(
      char      prompt[]   /* in  */,
      double    local_A[]  /* out */,
      int       m          /* in  */,
      int       local_m    /* in  */,
      int       n          /* in  */,
      int       my_rank    /* in  */,
      MPI_Comm  comm       /* in  */) {
   double* A = NULL;
   int local_ok = 1;

   if (my_rank == 0) {
      A = malloc(m * n * sizeof(double));
      if (A == NULL) local_ok = 0;
      Check_for_error(local_ok, "Read_matrix",
            "Can't allocate temporary matrix", comm);
      printf("Enter the matrix %s\n", prompt);
      for (int i = 0; i < m; i++)
         for (int j = 0; j < n; j++)
            scanf("%lf", &A[i*n+j]);
      MPI_Scatter(A, local_m*n, MPI_DOUBLE,
            local_A, local_m*n, MPI_DOUBLE, 0, comm);
      free(A);
   } else {
      Check_for_error(local_ok, "Read_matrix",
            "Can't allocate temporary matrix", comm);
      MPI_Scatter(A, local_m*n, MPI_DOUBLE,
            local_A, local_m*n, MPI_DOUBLE, 0, comm);
   }
}  /* Read_matrix */

void Read_vector(
      char      prompt[]     /* in  */,
      double    local_vec[]  /* out */,
      int       n            /* in  */,
      int       local_n      /* in  */,
      int       my_rank      /* in  */,
      MPI_Comm  comm         /* in  */) {
   double* vec = NULL;
   int local_ok = 1;

   if (my_rank == 0) {
      vec = malloc(n * sizeof(double));
      if (vec == NULL) local_ok = 0;
      Check_for_error(local_ok, "Read_vector",
            "Can't allocate temporary vector", comm);
      printf("Enter the vector %s\n", prompt);
      for (int i = 0; i < n; i++)
         scanf("%lf", &vec[i]);
      MPI_Scatter(vec, local_n, MPI_DOUBLE,
            local_vec, local_n, MPI_DOUBLE, 0, comm);
      free(vec);
   } else {
      Check_for_error(local_ok, "Read_vector",
            "Can't allocate temporary vector", comm);
      MPI_Scatter(vec, local_n, MPI_DOUBLE,
            local_vec, local_n, MPI_DOUBLE, 0, comm);
   }
}  /* Read_vector */

void Print_matrix(
      char      title[]    /* in */,
      double    local_A[]  /* in */,
      int       m          /* in */,
      int       local_m    /* in */,
      int       n          /* in */,
      int       my_rank    /* in */,
      MPI_Comm  comm       /* in */) {
   double* A = NULL;
   int i, j, local_ok = 1;

   if (my_rank == 0) {
      A = malloc(m * n * sizeof(double));
      if (A == NULL) local_ok = 0;
      Check_for_error(local_ok, "Print_matrix",
            "Can't allocate temporary matrix", comm);
      MPI_Gather(local_A, local_m*n, MPI_DOUBLE,
            A, local_m*n, MPI_DOUBLE, 0, comm);
      printf("\nThe matrix %s\n", title);
      for (i = 0; i < m; i++) {
         for (j = 0; j < n; j++)
            printf("%f ", A[i*n+j]);
         printf("\n");
      }
      printf("\n");
      free(A);
   } else {
      Check_for_error(local_ok, "Print_matrix",
            "Can't allocate temporary matrix", comm);
      MPI_Gather(local_A, local_m*n, MPI_DOUBLE,
            A, local_m*n, MPI_DOUBLE, 0, comm);
   }
}  /* Print_matrix */

void Print_vector(
      char      title[]     /* in */,
      double    local_vec[] /* in */,
      int       n           /* in */,
      int       local_n     /* in */,
      int       my_rank     /* in */,
      MPI_Comm  comm        /* in */) {
   double* vec = NULL;
   int local_ok = 1;

   if (my_rank == 0) {
      vec = malloc(n * sizeof(double));
      if (vec == NULL) local_ok = 0;
      Check_for_error(local_ok, "Print_vector",
            "Can't allocate temporary vector", comm);
      MPI_Gather(local_vec, local_n, MPI_DOUBLE,
            vec, local_n, MPI_DOUBLE, 0, comm);
      printf("\nThe vector %s\n", title);
      for (int i = 0; i < n; i++)
         printf("%f ", vec[i]);
      printf("\n");
      free(vec);
   }  else {
      Check_for_error(local_ok, "Print_vector",
            "Can't allocate temporary vector", comm);
      MPI_Gather(local_vec, local_n, MPI_DOUBLE,
            vec, local_n, MPI_DOUBLE, 0, comm);
   }
}  /* Print_vector */

void Mat_vect_mult(
      double    local_A[]  /* in  */,
      double    local_x[]  /* in  */,
      double    local_y[]  /* out */,
      int       local_m    /* in  */,
      int       n          /* in  */,
      int       local_n    /* in  */,
      MPI_Comm  comm       /* in  */) {
   double* x;
   int local_ok = 1;

   x = malloc(n * sizeof(double));
   if (x == NULL) local_ok = 0;
   Check_for_error(local_ok, "Mat_vect_mult",
         "Can't allocate temporary vector", comm);
   MPI_Allgather(local_x, local_n, MPI_DOUBLE,
         x, local_n, MPI_DOUBLE, comm);

   for (int local_i = 0; local_i < local_m; local_i++) {
      local_y[local_i] = 0.0;
      for (int j = 0; j < n; j++)
         local_y[local_i] += local_A[local_i*n+j] * x[j];
   }
   free(x);
}  /* Mat_vect_mult */