Using pthread to perform matrix multiplication
- by shadyabhi
I have both matrices containing only ones and each array has 500 rows and columns. So, the resulting matrix should be a matrix of all elements having value 500. But, I am getting res_mat[0][0]=5000. Even other elements are also 5000. Why?
#include<stdio.h>
#include<pthread.h>
#include<unistd.h>
#include<stdlib.h>
#define ROWS 500
#define COLUMNS 500
#define N_THREADS 10
int mat1[ROWS][COLUMNS],mat2[ROWS][COLUMNS],res_mat[ROWS][COLUMNS];
void *mult_thread(void *t)
{
/*This function calculates 50 ROWS of the matrix*/
int starting_row;
starting_row = *((int *)t);
starting_row = 50 * starting_row;
int i,j,k;
for (i = starting_row;i<starting_row+50;i++)
for (j=0;j<COLUMNS;j++)
for (k=0;k<ROWS;k++)
res_mat[i][j] += (mat1[i][k] * mat2[k][j]);
return;
}
void fill_matrix(int mat[ROWS][COLUMNS])
{
int i,j;
for(i=0;i<ROWS;i++)
for(j=0;j<COLUMNS;j++)
mat[i][j] = 1;
}
int main()
{
int n_threads = 10; //10 threads created bcos we have 500 rows and one thread calculates 50 rows
int j=0;
pthread_t p[n_threads];
fill_matrix(mat1);
fill_matrix(mat2);
for (j=0;j<10;j++)
pthread_create(&p[j],NULL,mult_thread,&j);
for (j=0;j<10;j++)
pthread_join(p[j],NULL);
printf("%d\n",res_mat[0][0]);
return 0;
}
