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**NAME**

atanh, atanhf, atanhl - inverse hyperbolic tangent function

**SYNOPSIS**

#include<math.h>doubleatanh(doublex);floatatanhf(floatx);longdoubleatanhl(longdoublex);Link with-lm. Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):atanh(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEatanhf(),atanhl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

**DESCRIPTION**

These functions calculate the inverse hyperbolic tangent ofx; that is the value whose hyperbolic tangent isx.

**RETURN** **VALUE**

On success, these functions return the inverse hyperbolic tangent ofx. Ifxis a NaN, a NaN is returned. Ifxis +0 (-0), +0 (-0) is returned. Ifxis +1 or -1, a pole error occurs, and the functions returnHUGE_VAL,HUGE_VALF, orHUGE_VALL, respectively, with the mathematically correct sign. If the absolute value ofxis greater than 1, a domain error occurs, and a NaN is returned.

**ERRORS**

Seemath_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur: Domain error:xless than -1 or greater than +1errnois set toEDOM. An invalid floating-point exception (FE_INVALID) is raised. Pole error:xis +1 or -1errnois set toERANGE(but see BUGS). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

**ATTRIBUTES**

For an explanation of the terms used in this section, seeattributes(7). ┌─────────────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├─────────────────────────────┼───────────────┼─────────┤ │atanh(),atanhf(),atanhl() │ Thread safety │ MT-Safe │ └─────────────────────────────┴───────────────┴─────────┘

**CONFORMING** **TO**

C99, POSIX.1-2001, POSIX.1-2008. The variant returningdoublealso conforms to SVr4, 4.3BSD.

**BUGS**

In glibc 2.9 and earlier, when a pole error occurs,errnoas set toEDOMinstead of the POSIX-mandatedERANGE. Since version 2.10, glibc does the right thing.

**SEE** **ALSO**

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

**COLOPHON**

This page is part of release 4.15 of the Linuxman-pagesproject. 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/. 2017-09-15 ATANH(3)