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
Thread	Yes