bessel_I1

Evaluates the real modified Bessel function of the first kind of order one I1(x).

Synopsis

#include <imsl.h>

float imsl_f_bessel_I1 (float x)

The type double procedure is imsl_d_bessel_I1.

Required Arguments

float x (Input)
Point at which the Bessel function is to be evaluated.

Return Value

The value of the Bessel function

 

If no solution can be computed, NaN is returned.

Description

For large |x|, imsl_f_bessel_I1 will overflow. It will underflow near zero.

Example

The Bessel function I1(1.5) is evaluated.

 

#include <imsl.h>

#include <stdio.h>

 

int main()

{

float x = 1.5;

float ans;

 

ans = imsl_f_bessel_I1(x);

printf("I1(%f) = %f\n", x, ans);

}

Output

 

I1(1.500000) = 0.981666

Alert Errors

IMSL_SMALL_ABS_ARG_UNDERFLOW

The argument should not be so close to zero that I1(x) ≈ x/2 underflows.

Fatal Errors

IMSL_LARGE_ABS_ARG_FATAL

The absolute value of x must not be so large that e|x| overflows.