C GSL贝塞尔函数示例

Question

I tried the following code:

# include <stdio.h> 
# include <gsl/gsl_sf_bessel.h> 
int main (void)
{
double x = 5.0; 
double y = gsl_sf_bessel_j0 (x); 
printf ("JO(%g) =  %.18e\n", x , y);
return(0);
}

the result I get is:

JO(5) =  -1.917848549326277019e-01

The result given in the GSL manual is

-1.775967713143382920e-01 

Any idea what is wrong?

Answer 1

It's indeed looks like a bug to me. I seems that it has not been fixed yet according to the changelist . However, there are two possible reasons:

• A typo in the documentation. Instead of gsl_sf_bessel_j0 you should use gsl_sf_bessel_J0 (very strange naming). That gives you JO(5) = -1.775967713143382642e-01 which is close enough to the desired answer (I'm not sure about the precision though).
• The documentation is correct, we need to fix the function itself.

Anyway, since it's not been reported I've submitted a bug report. I do plan to update this answer as soon as I get any information related to this problem.