Question

I’m trying to multiply two matrices using vecLibs’ cblas:

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#include <vecLib/cblas.h>

int main (void) {

    float *A = malloc(sizeof(float) *  2 * 3);
    float *B = malloc(sizeof(float) *  3 * 1);
    float *C = malloc(sizeof(float) *  2 * 1);

    cblas_sgemm(CblasRowMajor, 
                CblasNoTrans,
                CblasNoTrans, 
                2,
                1,
                3,
                1.0,
                A, 2,
                B, 3,
                0.0,
                C, 2);

    printf ("[ %f, %f]\n", C[0], C[1]);

    return 0;  
}

According to the docs every argument seems to match yet I get this error:

lda must be >= MAX(K,1): lda=2 K=3BLAS error: Parameter number 9 passed to cblas_sgemm had an invalid value

Answer 1

The error you are seeing seems perfectly correct to my eyes.

LDA is always the pitch of the array A in linear memory. If you are using row major storage order, the pitch will be the number of columns, not the number of rows. So LDA should be 3 in this case.