/*******************************************************************************/
/* BLAS ddot and dgemv
   ==================
   
   Compilation:  see the Makefile
   *********** 

******************************************************************************/   


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

#define N 10000

int main()
{  int i,j;
   static double x[N],b[N],A[N][N];
   double ddot_(int*,double*,int*,double*,int*);
   void dgemv_(char*,int*,int*,double*,double*,int*,double*,int*,double*,double*,int*);
   clock_t clock0, clock1;

   for (i=0; i<N; i++) 
   {  x[i]=1; b[i]=0;}
   
   for (i=0; i<N; i++) 
     for (j=0; j<N; j++) A[i][j]=i+j;
   
/* Standard loop
   *************/
   clock0 = clock();
   ...
   ...
   clock1 = clock();
   printf("CPU time loop:  %g miliseconds.\n",
        (1000*(double)(clock1 - clock0))/CLOCKS_PER_SEC);
	
/* Use Blas ddot
   *************/
   int n=N, inc=1;
   clock0 = clock();
   ...  
   clock1 = clock();
   printf("CPU time ddot:  %g miliseconds.\n",
        (1000*(double)(clock1 - clock0))/CLOCKS_PER_SEC);
        
/* Use Blas dgemv
   **************/
   clock0 = clock();
   char trans='N';
   double alpha=1, beta=0;
   ...
   clock1 = clock();
   printf("CPU time dgemv:  %g miliseconds.\n",
        (1000*(double)(clock1 - clock0))/CLOCKS_PER_SEC);
        
   return 0;
    
}