1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)atan.3 8.1 (Berkeley) 06/04/93 7.\" 8.Dd 9.Dt ATAN 3 10.Os 11.Sh NAME 12.Nm atan 13.Nd arc tangent function of one variable 14.Sh SYNOPSIS 15.Fd #include <math.h> 16.Ft double 17.Fn atan "double x" 18.Sh DESCRIPTION 19The 20.Fn atan 21function computes the principal value of the arc tangent of 22.Fa x . 23For a discussion of error due to roundoff, see 24.Xr math 3 . 25.Sh RETURN VALUES 26The 27.Fn atan 28function returns the arc tangent in the range 29.Bk -words 30.Bq -\*(Pi/2 , +\*(Pi/2 31.Ek 32radians. 33.Sh SEE ALSO 34.Xr acos 3 , 35.Xr asin 3 , 36.Xr atan2 3 , 37.Xr cos 3 , 38.Xr cosh 3 , 39.Xr sin 3 , 40.Xr sinh 3 , 41.Xr tan 3 , 42.Xr tanh 3 , 43.Xr math 3 , 44.Sh STANDARDS 45The 46.Fn atan 47function conforms to 48.St -ansiC . 49