In some cases it may be advantageous to pass problem-specific data to a user-supplied function through the IMSL C Math Library interface. This ability can be useful if a user-supplied function requires data that is local to the user's calling function, and the user wants to avoid using global data to allow the user-supplied function to access the data. Functions in IMSL C Math Library that accept user-supplied functions have an optional argument(s) that will accept an alternative user-supplied function, along with a pointer to the data, that allows user-specified data to be passed to the function. The example below demonstrates this feature using the IMSL C Math Library function imsl_f_min_uncon and optional argument IMSL_FCN_W_DATA.
#include <imsl.h>
#include <math.h>
#include <stdio.h>
static float fcn_w_data(float x, void *data);
int main()
{
float a = -100.0;
float b = 100.0;
float fx, x;
float usr_data[] = {5.0, 10.0};
x = imsl_f_min_uncon (NULL, a, b,
IMSL_FCN_W_DATA, fcn_w_data, usr_data,
0);
fx = fcn_w_data(x, (void*)usr_data);
printf ("The solution is: %8.4f\n", x);
printf ("The function evaluated at the solution is: %8.4f\n", fx);
}
/*
* User function that accepts additional data in a (void*) pointer.
* This (void*) pointer can be cast to any type and dereferenced to
* get at any sort of data-type or structure that is needed.
* For example, to get at the data in this example
* *((float*)data) and usr_data[0] contains the value 5.0
* *((float*)data+1) and usr_data[1] contains the value 10.0
*/
static float fcn_w_data(float x, void *data)
{
float *usr_data = (float*)data;
return exp(x) - usr_data[0]*x + usr_data[1];
}
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