1.\" Copyright (c) 1991 Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)acosh.3 5.2 (Berkeley) 5/6/91 33.\" 34.Dd May 6, 1991 35.Dt ACOSH 3 36.Os BSD 4.3 37.Sh NAME 38.Nm acosh 39.Nd inverse hyperbolic cosine function 40.Sh SYNOPSIS 41.Fd #include <math.h> 42.Ft double 43.Fn acosh "double x" 44.Sh DESCRIPTION 45The 46.Fn acosh 47function computes the inverse hyperbolic cosine 48of the real 49argument 50.Ar x . 51For a discussion of error due to roundoff, see 52.Xr math 3 . 53.Sh RETURN VALUES 54The 55.Fn acosh 56function 57returns the inverse hyperbolic cosine of 58.Ar x . 59On the 60.Tn VAX 61and 62.Tn Tahoe , 63if the argument is less than one 64.Fn acosh 65sets the global variable 66.Va errno 67to 68.Er EDOM 69and 70causes a reserved operand fault. 71.Sh SEE ALSO 72.Xr asinh 3 , 73.Xr atanh 3 , 74.Xr exp 3 , 75.Xr infnan 3 76.Xr math 3 , 77.Sh HISTORY 78The 79.Fn acosh 80function appeared in 81.Bx 4.3 . 82