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>

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.

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