1.\" Copyright (c) 1991 The 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.\" 4. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" from: @(#)atan.3 5.1 (Berkeley) 5/2/91 29.\" $FreeBSD$ 30.\" 31.Dd July 31, 2008 32.Dt ATAN 3 33.Os 34.Sh NAME 35.Nm atan , 36.Nm atanf , 37.Nm atanl 38.Nd arc tangent functions of one variable 39.Sh LIBRARY 40.Lb libm 41.Sh SYNOPSIS 42.In math.h 43.Ft double 44.Fn atan "double x" 45.Ft float 46.Fn atanf "float x" 47.Ft long double 48.Fn atanl "long double x" 49.Sh DESCRIPTION 50The 51.Fn atan , 52.Fn atanf , 53and 54.Fn atanl 55functions compute the principal value of the arc tangent of 56.Fa x . 57.Sh RETURN VALUES 58These functions return the arc tangent in the range 59.Bk -words 60.Bq -\*(Pi/2 , +\*(Pi/2 61.Ek 62radians. 63.Sh SEE ALSO 64.Xr acos 3 , 65.Xr asin 3 , 66.Xr atan2 3 , 67.Xr cos 3 , 68.Xr cosh 3 , 69.Xr math 3 , 70.Xr sin 3 , 71.Xr sinh 3 , 72.Xr tan 3 , 73.Xr tanh 3 74.Sh STANDARDS 75The 76.Fn atan , 77.Fn atanf , 78and 79.Fn atanl 80functions conform to 81.St -isoC-99 . 82