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 May 2, 1991 32.Dt ATAN 3 33.Os 34.Sh NAME 35.Nm atan , 36.Nm atanf 37.Nd arc tangent functions of one variable 38.Sh LIBRARY 39.Lb libm 40.Sh SYNOPSIS 41.In math.h 42.Ft double 43.Fn atan "double x" 44.Ft float 45.Fn atanf "float x" 46.Sh DESCRIPTION 47The 48.Fn atan 49and the 50.Fn atanf 51functions compute the principal value of the arc tangent of 52.Fa x . 53For a discussion of error due to roundoff, see 54.Xr math 3 . 55.Sh RETURN VALUES 56The 57.Fn atan 58and the 59.Fn atanf 60function returns the arc tangent in the range 61.Bk -words 62.Bq -\*(Pi/2 , +\*(Pi/2 63.Ek 64radians. 65.Sh SEE ALSO 66.Xr acos 3 , 67.Xr asin 3 , 68.Xr atan2 3 , 69.Xr cos 3 , 70.Xr cosh 3 , 71.Xr math 3 , 72.Xr sin 3 , 73.Xr sinh 3 , 74.Xr tan 3 , 75.Xr tanh 3 76.Sh STANDARDS 77The 78.Fn atan 79function conforms to 80.St -isoC . 81