3. Library calls (functions within program libraries)
ATANH
Section: Linux Programmer's Manual (3)Updated: 20150419
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NAME
atanh, atanhf, atanhl  inverse hyperbolic tangent functionSYNOPSIS
#include <math.h> double atanh(double x);Link with lm.
float atanhf(float x);
long double atanhl(long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
atanh():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 500 
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
atanhf(), atanhl():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
DESCRIPTION
These functions calculate the inverse hyperbolic tangent of x; that is the value whose hyperbolic tangent is x.RETURN VALUE
On success, these functions return the inverse hyperbolic tangent of x.If x is a NaN, a NaN is returned.
If x is +0 (0), +0 (0) is returned.
If x is +1 or 1, a pole error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathematically correct sign.
If the absolute value of x is greater than 1, a domain error occurs, and a NaN is returned.
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 less than 1 or greater than +1
 errno is set to EDOM. An invalid floatingpoint exception (FE_INVALID) is raised.
 Pole error: x is +1 or 1
 errno is set to ERANGE (but see BUGS). A dividebyzero floatingpoint exception (FE_DIVBYZERO) is raised.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface  Attribute  Value 
atanh(), atanhf(), atanhl()  Thread safety  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.The variant returning double also conforms to SVr4, 4.3BSD, C89.
BUGS
In glibc 2.9 and earlier, when a pole error occurs, errno as set to EDOM instead of the POSIXmandated ERANGE. Since version 2.10, glibc does the right thing.SEE ALSO
acosh(3), asinh(3), catanh(3), cosh(3), sinh(3), tanh(3)COLOPHON
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