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()
etc. and
y0l()
etc. functions are versions that take and return
float
and
long double
values, respectively.

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
(but see BUGS).
No
FE_DIVBYZERO
exception is returned by
fetestexcept(3)
for this case.

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 not set for this case.
An overflow floating-point exception
(FE_OVERFLOW)
is raised.

CONFORMING TO

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

BUGS

On a pole error, these functions set
errno
to
EDOM,
instead of
ERANGE
as POSIX.1-2004 requires.

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.

This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.