# Bessel1st

Advanced Analysis Library Only

double Bessel1st (double r, double x);

## Purpose

Computes the Bessel function Jr(x) of the first kind of fractional order r, which is defined as follows:

The Bessel function is a solution of the following differential equation:

For any integer value of order r, the function is defined for all real values of x. Otherwise, the function is defined for nonnegative real values of x.

## Parameters

Input
Name | Type | Description
r | double-precision | The order of the function.
x | double-precision | The point at which the Bessel function is evaluated.

## Return Value

Name | Type | Description
result | double-precision | The value of the Bessel function evaluated at x.