# jn(), jnf()

Compute a Bessel function of the first kind of a given order

## Synopsis:

```#include <math.h>

double jn( int n, double x );

float jnf( int n, float x );
```

## Arguments:

n, x
The numbers that you want to compute the Bessel function for.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

These functions compute the Bessel function for x of the first kind of order n.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

• Call feclearexcept(FE_ALL_EXCEPT) before calling jn() or jnf().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

## Returns:

The Bessel value of x of the first kind of order n.

If: These functions return: Errors:
x is NaN NaN
The correct result would cause underflow 0.0 FE_UNDERFLOW

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

## Examples:

```#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
int except_flags;
double x, y, z;

feclearexcept(FE_ALL_EXCEPT);

x = j0( 2.4 );

except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

feclearexcept(FE_ALL_EXCEPT);

y = y1( 1.58 );

except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

feclearexcept(FE_ALL_EXCEPT);

z = jn( 3, 2.4 );

except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

printf( "j0(2.4) = %f, y1(1.58) = %f\n", x, y );
printf( "jn(3,2.4) = %f\n", z );

return EXIT_SUCCESS;
}
```

## Classification:

jn() is POSIX 1003.1 XSI; jnf() is Unix

Safety:
Cancellation point No
Interrupt handler No
Signal handler No