/* dangerous due to misalignment problems */
B = (double **)
     malloc(m*sizeof(double *)+m*n*sizeof(double));
if ( B == NULL ) return NULL;
B[0] = (double *)(B[m]);
/* now set the other pointers */
for ( i = 1; i < m; i++ )
  B[i] = B[0] + i*n;