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Section: Linux Programmer's Manual (3)
Updated: 2020-06-09
Page Index

NAME

y0, y0f, y0l, y1, y1f, y1l, yn, ynf, ynl - Bessel functions of the second kind

SYNOPSIS

#include <math.h>

double y0(double x);
double y1(double x);
double yn(int n, double x);

float y0f(float x);
float y1f(float x);
float ynf(int n, float x);

long double y0l(long double x);
long double y1l(long double x);
long double ynl(int n, long double x);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

y0(), y1(), yn():

: _XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

y0f(), y0l(), y1f(), y1l(), ynf(), ynl():

: _XOPEN_SOURCE >= 600
    || (_ISOC99_SOURCE && _XOPEN_SOURCE)
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION

The y0() and y1() functions return Bessel functions of x of the second kind of orders 0 and 1, respectively. The yn() function returns the Bessel function of x of the second kind of order n.

The value of x must be positive.

The y0f(), y1f(), and ynf() functions are versions that take and return float values. The y0l(), y1l(), and ynl() functions are versions that take and return long double values.

RETURN VALUE

On success, these functions return the appropriate Bessel value of the second kind for x.

If x is a NaN, a NaN is returned.

If x is negative, a domain error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively. (POSIX.1-2001 also allows a NaN return for this case.)

If x is 0.0, a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

If the result underflows, a range error occurs, and the functions return 0.0

If the result overflows, a range error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively. (POSIX.1-2001 also allows a 0.0 return for this case.)

ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x is negative: errno is set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.
Pole error: x is 0.0: errno is set to ERANGE and an FE_DIVBYZERO exception is raised (but see BUGS).
Range error: result underflow: errno is set to ERANGE. No FE_UNDERFLOW exception is returned by fetestexcept(3) for this case.
Range error: result overflow: errno is set to ERANGE (but see BUGS). An overflow floating-point exception (FE_OVERFLOW) is raised.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface	Attribute	Value
y0(), y0f(), y0l()	Thread safety	MT-Safe
y1(), y1f(), y1l()	Thread safety	MT-Safe
yn(), ynf(), ynl()	Thread safety	MT-Safe

CONFORMING TO

The functions returning double conform to SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008. The others are nonstandard functions that also exist on the BSDs.

BUGS

Before glibc 2.19, these functions misdiagnosed pole errors: errno was set to EDOM, instead of ERANGE and no FE_DIVBYZERO exception was raised.

Before glibc 2.17, did not set errno for "range error: result underflow".

In glibc version 2.3.2 and earlier, these functions do not raise an invalid floating-point exception (FE_INVALID) when a domain error occurs.

COLOPHON

This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

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