'\" t .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk .\" .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" References consulted: .\" Linux libc source code .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) .\" 386BSD man pages .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu) .\" Modified 2002-07-27 by Walter Harms .\" (walter.harms@informatik.uni-oldenburg.de) .\" .TH atanh 3 2024-05-02 "Linux man-pages 6.9.1" .SH NAME atanh, atanhf, atanhl \- inverse hyperbolic tangent function .SH LIBRARY Math library .RI ( libm ", " \-lm ) .SH SYNOPSIS .nf .B #include .P .BI "double atanh(double " x ); .BI "float atanhf(float " x ); .BI "long double atanhl(long double " x ); .P .fi .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .P .BR atanh (): .nf _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE .fi .P .BR atanhf (), .BR atanhl (): .nf _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE .fi .SH DESCRIPTION These functions calculate the inverse hyperbolic tangent of .IR x ; that is the value whose hyperbolic tangent is .IR x . .SH RETURN VALUE On success, these functions return the inverse hyperbolic tangent of .IR x . .P If .I x is a NaN, a NaN is returned. .P If .I x is +0 (\-0), +0 (\-0) is returned. .P If .I x is +1 or \-1, a pole error occurs, and the functions return .BR HUGE_VAL , .BR HUGE_VALF , or .BR HUGE_VALL , respectively, with the mathematically correct sign. .P If the absolute value of .I x is greater than 1, a domain error occurs, and a NaN is returned. .\" .\" POSIX.1-2001 documents an optional range error for subnormal x; .\" glibc 2.8 does not do this. .SH ERRORS See .BR math_error (7) for information on how to determine whether an error has occurred when calling these functions. .P The following errors can occur: .TP Domain error: \fIx\fP less than \-1 or greater than +1 .I errno is set to .BR EDOM . An invalid floating-point exception .RB ( FE_INVALID ) is raised. .TP Pole error: \fIx\fP is +1 or \-1 .I errno is set to .B ERANGE (but see BUGS). A divide-by-zero floating-point exception .RB ( FE_DIVBYZERO ) is raised. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lbx lb lb l l l. Interface Attribute Value T{ .na .nh .BR atanh (), .BR atanhf (), .BR atanhl () T} Thread safety MT-Safe .TE .SH STANDARDS C11, POSIX.1-2008. .SH HISTORY C99, POSIX.1-2001. .P The variant returning .I double also conforms to SVr4, 4.3BSD. .SH BUGS In glibc 2.9 and earlier, .\" Bug: https://www.sourceware.org/bugzilla/show_bug.cgi?id=6759 .\" This can be seen in sysdeps/ieee754/k_standard.c when a pole error occurs, .I errno is set to .B EDOM instead of the POSIX-mandated .BR ERANGE . Since glibc 2.10, glibc does the right thing. .SH SEE ALSO .BR acosh (3), .BR asinh (3), .BR catanh (3), .BR cosh (3), .BR sinh (3), .BR tanh (3)