Return Values from User-Supplied Functions
All values returned by user-supplied functions must be valid real numbers. It is the user’s responsibility to check that the values returned by a user-supplied function do not contain NaN, infinity, or negative infinity values.
In addition to the techniques described below, it is also possible to instruct the IMSL C Numerical Library to return control to the calling program in case an unrecoverable error occurs within a user-supplied function. See function
imsl_set_user_fcn_return_flag for a description of this feature.
Example
#include <imsl.h>
#include <math.h>
void fcn(int, int, float[], float[]);
int main()
{
int m=3, n=1;
float *result, fx[3];
float xguess[]={1.0};
result = imsl_f_nonlin_least_squares(fcn, m, n, IMSL_XGUESS,
xguess, 0);
fcn(m, n, result, fx);
/* Print results */
imsl_f_write_matrix("The solution is", 1, 1, result, 0);
imsl_f_write_matrix("The function values are", 1, 3, fx, 0);
}
void fcn(int m, int n, float x[], float f[])
{
int i;
float y[3] = {2.0, 4.0, 3.0};
float t[3] = {1.0, 2.0, 3.0};
for (i=0; i<m; i++)
{
/* check for x=0
do not want to return infinity to nonlin_least_squares */
if (x[0] == 0.0) {
f[i] = 10000.;
} else {
f[i] = t[i]/x[0] - y[i];
}
}
}
