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Addition and Subtraction of Matrix using pthreads

  • Difficulty Level : Hard
  • Last Updated : 18 Apr, 2019

Addition or Subtraction of matrices takes O(n^2) time without threads but using threads we don’t reduce the time complexity of the program we divide the task into core like if we have 4 core then divide the matrix into 4 part and each core take one part of the matrix and compute the operations and finally when each task is complete then all 4 thread join the main program and show final output.

Note –This method only works when we have more then one CPU core if we have only one core the Don’t create the thread because we divide the task and perform on only one CPU so it is waste of time to dividing a task and then compute.

Examples:

Input : 

Matrix A:
3 7 3 6 
9 2 0 3 
0 2 1 7 
2 2 7 9 

Matrix B:
6 5 5 2 
1 7 9 6 
6 6 8 9 
0 3 5 2 

Output :

Sum of Matrix A and B:
9   12   8   8   
10   9   9   9   
6   8   9   16   
2   5   12   11   

Subtraction of Matrix A and B:
-3   2  -2   4   
 8  -5  -9  -3   
-6  -4  -7  -2   
 2  -1   2   7 



Code – It is advised to execute the program in Linux based system.




#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
  
// Value depend on System core
#define CORE 4
  
// Maximum matrix size
#define MAX 4
  
// Maximum threads is equal to total core of system
pthread_t thread[CORE * 2];
int mat_A[MAX][MAX], mat_B[MAX][MAX], sum[MAX][MAX], sub[MAX][MAX];
  
// Addition of a Matrix
void* addition(void* arg)
{
  
    int i, j;
    int core = (int)arg;
  
    // Each thread computes 1/4th of matrix addition
    for (i = core * MAX / 4; i < (core + 1) * MAX / 4; i++) {
  
        for (j = 0; j < MAX; j++) {
  
            // Compute Sum Row wise
            sum[i][j] = mat_A[i][j] + mat_B[i][j];
        }
  
    }
  
}
  
  
// Subtraction of a Matrix
void* subtraction(void* arg)
{
  
    int i, j;
    int core = (int)arg;
  
    // Each thread computes 1/4th of matrix subtraction
    for (i = core * MAX / 4; i < (core + 1) * MAX / 4; i++) {
  
        for (j = 0; j < MAX; j++) {
  
            // Compute Subtract row wise
            sub[i][j] = mat_A[i][j] - mat_B[i][j];
        }
  
    }
  
}
  
  
// Driver Code
int main()
{
  
    int i, j, step = 0;
    // Generating random values in mat_A and mat_B
    for (i = 0; i < MAX; i++)  {
  
        for (j = 0; j < MAX; j++)  {
  
            mat_A[i][j] = rand() % 10;
            mat_B[i][j] = rand() % 10;
  
        }
  
    }
  
  
    // Displaying mat_A
    printf("\nMatrix A:\n");
  
    for (i = 0; i < MAX; i++) {
  
        for (j = 0; j < MAX; j++) {
  
            printf("%d ", mat_A[i][j]);
        }
  
        printf("\n");
    }
  
    // Displaying mat_B
    printf("\nMatrix B:\n");
  
    for (i = 0; i < MAX; i++) {
  
        for (j = 0; j < MAX; j++) {
  
            printf("%d ", mat_B[i][j]);
        }
  
        printf("\n");
    }
  
    // Creating threads equal
    // to core size and compute matrix row
    for (i = 0; i < CORE; i++) {
  
        pthread_create(&thread[i], NULL, &addition, (void*)step);
        pthread_create(&thread[i + CORE], NULL, &subtraction, (void*)step);
        step++;
    }
  
    // Waiting for join threads after compute
    for (i = 0; i < CORE * 2; i++) {
  
        pthread_join(thread[i], NULL);
    }
  
    // Display Addition of mat_A and mat_B
    printf("\n Sum of Matrix A and B:\n");
  
    for (i = 0; i < MAX; i++) {
  
        for (j = 0; j < MAX; j++) {
  
            printf("%d   ", sum[i][j]);
        }
  
        printf("\n");
    }
  
    // Display Subtraction of mat_A and mat_B
    printf("\n Subtraction of Matrix A and B:\n");
  
    for (i = 0; i < MAX; i++) {
  
        for (j = 0; j < MAX; j++) {
  
            printf("%d   ", sub[i][j]);
        }
  
        printf("\n");
    }
  
    return 0;
}

Output:

Matrix A:
3 7 3 6 
9 2 0 3 
0 2 1 7 
2 2 7 9 

Matrix B:
6 5 5 2 
1 7 9 6 
6 6 8 9 
0 3 5 2 

Sum of Matrix A and B:

9   12   8   8   
10   9   9   9   
6   8   9   16   
2   5   12   11   

Subtraction of Matrix A and B:

-3   2  -2   4   
 8  -5  -9  -3   
-6  -4  -7  -2   
 2  -1   2   7 

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