/* Example to illustrate GEMM operation on submatrices.
   A is 6 X 10, B is 5 X 6, C is 6 X 8
   User wants to do C(2:5,5:6) = A(2:5,5:7) * B(2:4,2:3)
*/

#include <stdio.h>
#include <mkl.h>

int main(){
double A[6*10], B[5*6], C[6*8];
int m = 4, n = 2, k = 3,   ldA = 10, ldB = 6, ldC = 8;
// row and column counts :
int rA = 6, rB = 5, rC = 6, cA = 10,  cB = 6,  cC = 8;
// positions of first element of submatrices
int sA = 14, sB = 7, sC = 12;

double alpha=1.0, beta=0.0; int i,j;

for(i=0; i<rA; i++)for(j=0; j<cA; j++)A[ldA*i+j]=i*cA+j;
for(i=0; i<rB; i++)for(j=0; j<cB; j++)B[ldB*i+j]=i*cB+j;
for(i=0; i<rC; i++)for(j=0; j<cC; j++)C[ldC*i+j]=0;

cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans,
                m, n, k, alpha, A+sA, ldA, B+sB, ldB, beta, C+sC, ldC);

for(i=1; i<5; i++){
   for(j=4; j<6; j++)printf("%10.1f ",C[ldC*i+j]);
   printf("\n");
   }
}