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: The general-purpose math library.
libm-sve: (QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

If you want only selected processes to run with the SVE version, you can include both libraries in your OS image and use the -l m or -l m-sve option to qcc to link explicitly against the appropriate one.
If you want all processes to use the SVE version, include libm-sve.so in your OS image and set up a symbolic link from libm.so to libm-sve.so. Use the -l m option to qcc to link against the library.

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

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	Yes
Signal handler	Yes
Thread	Yes