多次元配列のallocate

double **mat;
int i, 
int n=5;

mat = (double **)calloc(n, sizeof(double));
for (i=0; i<n; i++) {
  mat[i] = (double *)calloc(n, sizeof(double));
}
...

if (mat[0]) free(mat[0]);
if (mat) free(mat);
...