.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
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.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" %%%LICENSE_END
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 19:08:17 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-08-25, aeb
.\" Modified 2004-11-12 as per suggestion by Fabian Kreutz/AEB
.\" 2008-07-24, mtk, created this page, based on material from j0.3.
.\"
.TH Y0 3  2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
y0, y0f, y0l, y1, y1f, y1l, yn, ynf, ynl \-
Bessel functions of the second kind
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.BI "double y0(double " x );
.BI "double y1(double " x );
.BI "double yn(int " n ", double " x );
.PP
.BI "float y0f(float " x );
.BI "float y1f(float " x );
.BI "float ynf(int " n ", float " x );
.PP
.BI "long double y0l(long double " x );
.BI "long double y1l(long double " x );
.BI "long double ynl(int " n ", long double " x );
.fi
.PP
Link with \fI\-lm\fP.
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.ad l
.BR y0 (),
.BR y1 (),
.BR yn ():
.RS 4
_XOPEN_SOURCE
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
.RE
.br
.BR y0f (),
.BR y0l (),
.BR y1f (),
.BR y1l (),
.BR ynf (),
.BR ynl ():
.RS 4
_XOPEN_SOURCE \ >=\ 600
    || (_ISOC99_SOURCE && _XOPEN_SOURCE)
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
.RE
.ad b
.SH DESCRIPTION
.PP
The
.BR y0 ()
and
.BR y1 ()
functions return Bessel functions of
.I x
of the second kind of orders 0 and 1, respectively.
The
.BR yn ()
function
returns the Bessel function of
.I x
of the second kind of order
.IR n .
.PP
The value of
.I x
must be positive.
.PP
The
.BR y0f (),
.BR y1f (),
and
.BR ynf ()
functions are versions that take and return
.I float
values.
The
.BR y0l (),
.BR y1l (),
and
.BR ynl ()
functions are versions that take and return
.I "long double"
values.
.SH RETURN VALUE
On success, these functions return the appropriate
Bessel value of the second kind for
.IR x .
.PP
If
.I x
is a NaN, a NaN is returned.
.PP
If
.I x
is negative,
a domain error occurs,
and the functions return
.RB - HUGE_VAL ,
.RB - HUGE_VALF ,
or
.RB - HUGE_VALL ,
respectively.
(POSIX.1-2001 also allows a NaN return for this case.)
.PP
If
.I x
is 0.0,
a pole error occurs,
and the functions return
.RB - HUGE_VAL ,
.RB - HUGE_VALF ,
or
.RB - HUGE_VALL ,
respectively.
.PP
If the result underflows,
a range error occurs,
and the functions return 0.0
.PP
If the result overflows,
a range error occurs,
and the functions return
.RB - HUGE_VAL ,
.RB - HUGE_VALF ,
or
.RB - HUGE_VALL ,
respectively.
(POSIX.1-2001 also allows a 0.0 return for this case.)
.SH ERRORS
See
.BR math_error (7)
for information on how to determine whether an error has occurred
when calling these functions.
.PP
The following errors can occur:
.TP
Domain error: \fIx\fP is negative
.I errno
is set to
.BR EDOM .
An invalid floating-point exception
.RB ( FE_INVALID )
is raised.
.TP
Pole error: \fIx\fP is 0.0
.\" Before POSIX.1-2001 TC2, this was (inconsistently) specified
.\" as a range error.
.I errno
is set to
.\" FIXME . y0(0.0) gives EDOM
.BR ERANGE
(but see BUGS).
No
.B FE_DIVBYZERO
exception is returned by
.BR fetestexcept (3)
for this case.
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6808
.TP
Range error: result underflow
.\" e.g., y0(1e33) on glibc 2.8/x86-32
.I errno
is set to
.BR ERANGE .
.\" An underflow floating-point exception
.\" .RB ( FE_UNDERFLOW )
.\" is raised.
.\" FIXME . Is it intentional that these functions do not use FE_*?
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6806
No
.B FE_UNDERFLOW
exception is returned by
.BR fetestexcept (3)
for this case.
.TP
Range error: result overflow
.\" e.g., yn(10, 1e-40) on glibc 2.8/x86-32
.\" .I errno
.\" is set to
.\" .BR ERANGE .
.I errno
is not set for this case.
.\" FIXME . Is it intentional that errno is not set?
.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6808
An overflow floating-point exception
.RB ( FE_OVERFLOW )
is raised.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR y0 (),
.BR y0f (),
.BR y0l ()
T}	Thread safety	MT-Safe
T{
.BR y1 (),
.BR y1f (),
.BR y1l ()
T}	Thread safety	MT-Safe
T{
.BR yn (),
.BR ynf (),
.BR ynl ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
The functions returning
.I double
conform to SVr4, 4.3BSD,
POSIX.1-2001, POSIX.1-2008.
The others are nonstandard functions that also exist on the BSDs.
.SH BUGS
On a pole error, these functions set
.I errno
to
.BR EDOM ,
instead of
.BR ERANGE
as POSIX.1-2004 requires.
.\" FIXME .
.\" Bug raised: http://sourceware.org/bugzilla/show_bug.cgi?id=6807
.PP
In glibc version 2.3.2 and earlier,
.\" FIXME . Actually, 2.3.2 is the earliest test result I have; so yet
.\" to confirm if this error occurs only in 2.3.2.
these functions do not raise an invalid floating-point exception
.RB ( FE_INVALID )
when a domain error occurs.
.SH SEE ALSO
.BR j0 (3)
.SH COLOPHON
This page is part of release 4.16 of the Linux
.I 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/.