DnC_Strassens's multiplication.c

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/*Time Complexity
STRASSEN'S MATRIX MULTIPLICATION*/

#include<stdio.h>
#include<time.h>

int main()
{
  	int a[2][2], b[2][2], c[2][2], i, j;
	clock_t start,end;
	double time;
  	int m1, m2, m3, m4 , m5, m6, m7;
 	printf("Enter the 4 elements of first matrix: ");
 	for(i = 0;i < 2; i++)
      		for(j = 0;j < 2; j++)
           			scanf("%d", &a[i][j]);
 	printf("Enter the 4 elements of second matrix: ");
  	for(i = 0; i < 2; i++)
      		for(j = 0;j < 2; j++)
           			scanf("%d", &b[i][j]);
 	printf("\nThe first matrix is\n");
  	for(i = 0; i < 2; i++)
	{
      		printf("\n");
      		for(j = 0; j < 2; j++)
           			printf("%d\t", a[i][j]);
  	}
	printf("\nThe second matrix is\n");
  	for(i = 0;i < 2; i++)
	{
      		printf("\n");
      		for(j = 0;j < 2; j++)
           			printf("%d\t", b[i][j]);
  	}
	start = clock();
 	m1= (a[0][0] + a[1][1]) * (b[0][0] + b[1][1]);
  	m2= (a[1][0] + a[1][1]) * b[0][0];
  	m3= a[0][0] * (b[0][1] - b[1][1]);
  	m4= a[1][1] * (b[1][0] - b[0][0]);
  	m5= (a[0][0] + a[0][1]) * b[1][1];
  	m6= (a[1][0] - a[0][0]) * (b[0][0]+b[0][1]);
  	m7= (a[0][1] - a[1][1]) * (b[1][0]+b[1][1]);
  	c[0][0] = m1 + m4- m5 + m7;
  	c[0][1] = m3 + m5;
  	c[1][0] = m2 + m4;
  	c[1][1] = m1 - m2 + m3 + m6;
 	printf("\nAfter multiplication using Strassen's algorithm \n");
   	for(i = 0; i < 2 ; i++)
	{
      		printf("\n");
      		for(j = 0;j < 2; j++)
           			printf("%d\t", c[i][j]);
   	}
	end = clock();
	time = (double)((start - end)/CLOCKS_PER_SEC);
	printf("Time taken by Strassen's Multiplication is : %f",time);
 	return 0;
}

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