How to use the function ‘cblas_dgemm_compute’ of mkl?

[lianchen]

Are there any examples showing how to use those functions: cblas_dgemm_pack_get_size(), cblas_dgemm_pack(), cblas_dgemm_compute() ? I would like to realize a specialized GEMM with a packed matrix B. Thanks.

This is my code. I have two questions：

①The function cblas_dgemm_pack_get_size() returns a very large number 7767808 when I want to pack the matrix B whose element type is double and dimension equals to 256 * 256. 

②The difference between C1 and C2 is larger than 1.0e-6. 

int main(int argc, const char* argv[])

{

    // matrix parameters

    int M, N, K;

    int LDA, LDB, LDC;

    printf("[INPUT] input M N K\n");

    if(scanf("%d %d %d", &M, &N, &K) == 3){

        printf("[TRUE] true parameters for scanf\n");

    }

    else{

        printf("[FALSE] false parameters for scanf\n");

        exit(EXIT_FAILURE);

    }

    // matrix buffer, column major

    LDA = M, LDB = K, LDC = M;

    double *A = NULL,

                  *B = NULL, *B_PACK = NULL,

                  *C1 = NULL, *C2 = NULL;

    double alpha = 0.000001, beta = 0.000001;

    A = (double *) malloc (sizeof(double) * M * K);

    B = (double *) malloc (sizeof(double) * K * N);

    C1 = (double *) malloc (sizeof(double) * M * N);

    C2 = (double *) malloc (sizeof(double) * M * N);

    gen_matrix(A, M, K), gen_matrix(B, K, N), gen_matrix(C1, M, N);    // initialize matrix A、B、C1

    matrix_copy(C1, M, N, C2);  // copy the value from C1 to C2

    B_PACK = (double *) malloc (cblas_dgemm_pack_get_size(CblasBMatrix, M, N, K));

    cblas_dgemm_pack(CblasColMajor, CblasBMatrix, CblasNoTrans, M, N, K, alpha,   B, LDB, B_PACK);

    cblas_dgemm(CblasColMajor, CblasNoTrans, CblasNoTrans, M, N, K, alpha, A, LDA, B, LDB, beta, C1, LDC);

    cblas_dgemm_compute(CblasColMajor, CblasNoTrans, CblasNoTrans, M, N, K, A, LDA, B_PACK , LDB, beta, C2, LDC);

    double diff = max_abs_diff(M, N, C1, LDC, C2, LDC);

    printf("diff = %lf\n", diff);  // returns the maximum absolute difference over

                                                    // corresponding elements of matrices A and B.

    return 0;

}