Question about (double *)NULL

Umfpack is a C library for computations dealing with sparse
matrices. Several examples in the User's Guide use a certain
cast that puzzles me. Here is an example.

The prototype of the function umfpack_di_symbolic() is:

int umfpack_di_symbolic
(
int n_row,
int n_col,
const int Ap [ ],
const int Ai [ ],
const double Ax [ ],
void **Symbolic,
const double Control [UMFPACK_CONTROL],
double Info [UMFPACK_INFO]
);

The header file umfpack.h has:
#define UMFPACK_CONTROL 20

Here is a sample usage:

int main (void)
{
double *null = (double *) NULL ;
...
(void) umfpack_di_symbolic (n, n, Ap, Ai, Ax, &Symbolic, null, null) ;
...
return (0) ;
}

(Code fragments are put here by "cut-and-paste"ing from the manual.)

My question is: Does the cast in (double *)NULL accomplish anything?
It seems to me that the call to umfpack_di_symbolic() equivalent to:

umfpack_di_symbolic (n, n, Ap, Ai, Ax, &Symbolic, NULL, NULL) ;

Comments?

--
Rouben Rostamian
.

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