atanh man page

atanh, atanhf, atanhl — inverse hyperbolic tangent function


#include <math.h>

double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);

Link with -lm.

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


   || _XOPEN_SOURCE >= 500
   || /* Since glibc 2.19: */ _DEFAULT_SOURCE
   || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

atanhf(), atanhl():

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


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.


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 floating-point exception (FE_INVALID) is raised.

Pole error: x is +1 or -1

errno is set to ERANGE (but see Bugs). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.


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

Interface Attribute Value
atanh(), atanhf(), atanhl() Thread safety MT-Safe

Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD.


In glibc 2.9 and earlier, when a pole error occurs, errno as set to EDOM instead of the POSIX-mandated ERANGE. Since version 2.10, glibc does the right thing.

See Also

acosh(3), asinh(3), catanh(3), cosh(3), sinh(3), tanh(3)


This page is part of release 4.15 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

Referenced By

acosh(3), asinh(3), catanh(3), cosh(3), sinh(3), tanh(3).

The man pages atanhf(3) and atanhl(3) are aliases of atanh(3).

2017-09-15 Linux Programmer's Manual