ATANH(3) (2017-09-15) ATANH(3) NAME atanh, atanhf, atanhl - inverse hyperbolic tangent function SYNOPSIS #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)): atanh(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE atanhf(), 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 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. Page 1 Plan 9 (printed 5/17/22) ATANH(3) (2017-09-15) ATANH(3) The following errors can occur: Domain error: x less than -1 or greater than +1 errno is set to EDOM. An invalid floating-point excep- tion (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. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). allbox; lbw28 lb lb l l l. Interface Attribute Value T{ atanh(), atanhf(), atanhl() T} Thread safety MT-Safe CONFORMING TO C99, POSIX.1-2001, POSIX.1-2008. The variant returning double also conforms to SVr4, 4.3BSD. BUGS 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) COLOPHON This page is part of release 5.10 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 https://www.kernel.org/doc/man-pages/. Page 2 Plan 9 (printed 5/17/22)