jn(), jnf()

Compute a Bessel function of the first kind

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 computes the Bessel function of the first kind for n and x.

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

Returns:

The result of the Bessel function of n and x.

If x argument is too large in magnitude, or the correct result would cause an underflow, 0 is returned, and a range error may occur. If x is NaN, NaN is returned.

Errors:

FE_UNDERFLOW
The value of x is too large in magnitude, or an underflow occurred.

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_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    feclearexcept(FE_ALL_EXCEPT);

    y = y1( 1.58 );

    except_flags = fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    feclearexcept(FE_ALL_EXCEPT);

    z = jn( 3, 2.4 );

    except_flags = fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    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