#include <stdlib.h>

double** dmalloc_2d(int m, int n);
void dfree_2d(double **A);

// allocate a double-precision m x n matrix
double** dmalloc_2d(int m, int n) {
    if (m <= 0 || n <= 0) return NULL;
    double **A = malloc(m * sizeof(double *));
    if (A == NULL) return NULL;
    A[0] = malloc(m*n*sizeof(double));
    if (A[0] == NULL) {
        free(A);
        return NULL;
    }
    for (int i = 1; i < m; i++)
        A[i] = A[0] + i * n;
    return A;
}

// de-allocating memory, allocated with dmalloc_2d
void dfree_2d(double **A) {
    free(A[0]);
    free(A);
}