Answer Happy

Convert the following code to use MPI_Scatter and/or
MPI_Reduce.
#include <stdio.h>
#include <mpi.h>
#include <stdlib.h>
#define max_rows 100000
#define send_data_tag 2001
#define return_data_tag 2002
int array[max_rows];
int array2[max_rows];
main(int argc, char **argv)
{
long int sum, partial_sum;
MPI_Status status;
int my_id, root_process, ierr, i, num_rows,
num_procs,
an_id, num_rows_to_receive,
avg_rows_per_process,
sender, num_rows_received,
start_row, end_row, num_rows_to_send;
/* Now replicate this process to create
parallel processes.
* From this point on, every process
executes a seperate copy
* of this program */
ierr = MPI_Init(&argc, &argv);
root_process = 0;
/*.........Find out process
id and how many processes were started...........*/
ierr = MPI_Comm_rank(MPI_COMM_WORLD,
&my_id);
ierr = MPI_Comm_size(MPI_COMM_WORLD,
&num_procs);
if(my_id == root_process) {
printf("Enter number ");
scanf("%i",
&num_rows);
if(num_rows > max_rows)
{
printf("Too many
numbers.\n");
exit(1);
}
avg_rows_per_process =
num_rows / num_procs;
/* initialize an array */
for(i = 0; i < num_rows;
i++) {
array = i + 1;
}
for(an_id = 1; an_id <
num_procs; an_id++) {
start_row =
an_id*avg_rows_per_process + 1;
end_row =
(an_id + 1)*avg_rows_per_process;
if((num_rows -
end_row) < avg_rows_per_process)
end_row =
num_rows - 1;
num_rows_to_send =
end_row - start_row + 1;
ierr = MPI_Send(
&num_rows_to_send, 1 , MPI_INT,
an_id, send_data_tag, MPI_COMM_WORLD);
ierr = MPI_Send(
&array[start_row], num_rows_to_send, MPI_INT,
an_id, send_data_tag, MPI_COMM_WORLD);
}
/* calculate the sum of the
values in the segment assigned
* to the root process */
sum = 0;
for(i = 0; i <
avg_rows_per_process + 1; i++) {
sum += array;
}
printf("sum %i calculated by
root process\n", sum);
for(an_id = 1; an_id < num_procs;
an_id++) {
ierr = MPI_Recv(
&partial_sum, 1, MPI_LONG, MPI_ANY_SOURCE,
return_data_tag, MPI_COMM_WORLD, &status);
sender =
status.MPI_SOURCE;
printf("Partial sum %i
returned from process %i\n", partial_sum, sender);
sum +=
partial_sum;
}
printf("The grand total is:
%i\n", sum);
}
else {
ierr = MPI_Recv(
&num_rows_to_receive, 1, MPI_INT,
root_process, send_data_tag, MPI_COMM_WORLD,
&status);
ierr = MPI_Recv( &array2,
num_rows_to_receive, MPI_INT,
root_process, send_data_tag, MPI_COMM_WORLD,
&status);
num_rows_received =
num_rows_to_receive;
partial_sum = 0;
for(i = 0; i <
num_rows_received; i++) {
partial_sum +=
array2;
}
ierr = MPI_Send( &partial_sum,
1, MPI_LONG, root_process,
return_data_tag, MPI_COMM_WORLD);
}
/*..............Clean up all
MPI state before exit of process.............*/
ierr = MPI_Finalize();
}