1.\" Copyright (c) 1985, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.roff% 5.\" 6.\" @(#)atanh.3 8.1 (Berkeley) 06/04/93 7.\" 8.Dd 9.Dt ATANH 3 10.Os BSD 4.3 11.Sh NAME 12.Nm atanh 13.Nd inverse hyperbolic tangent function 14.Sh SYNOPSIS 15.Fd #include <math.h> 16.Ft double 17.Fn atanh "double x" 18.Sh DESCRIPTION 19The 20.Fn atanh 21function computes the inverse hyperbolic tangent 22of the real 23argument 24.Ar x . 25For a discussion of error due to roundoff, see 26.Xr math 3 . 27.Sh RETURN VALUES 28The 29.Fn atanh 30function 31returns the inverse hyperbolic tangent of 32.Ar x 33if successful. 34On the 35.Tn VAX 36and 37.Tn Tahoe , 38if the argument has absolute value 39bigger than or equal to 1, 40.Fn atanh 41sets the global variable 42.Va errno 43to 44.Er EDOM 45and 46a reserved operand fault is generated. 47.Sh SEE ALSO 48.Xr acosh 3 , 49.Xr asinh 3 , 50.Xr exp 3 , 51.Xr infnan 3 52.Xr math 3 , 53.Sh HISTORY 54The 55.Fn atanh 56function appeared in 57.Bx 4.3 . 58