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+'\" t
+.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
+.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" References consulted:
+.\"     Linux libc source code
+.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
+.\"     386BSD man pages
+.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
+.\" Modified 2002-07-27 by Walter Harms
+.\" 	(walter.harms@informatik.uni-oldenburg.de)
+.\"
+.TH atan 3 (date) "Linux man-pages (unreleased)"
+.SH NAME
+atan, atanf, atanl \- arc tangent function
+.SH LIBRARY
+Math library
+.RI ( libm ", " \-lm )
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.P
+.BI "double atan(double " x );
+.BI "float atanf(float " x );
+.BI "long double atanl(long double " x );
+.P
+.fi
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR atanf (),
+.BR atanl ():
+.nf
+    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
+        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.fi
+.SH DESCRIPTION
+These functions calculate the principal value of the arc tangent of
+.IR x ;
+that is the value whose tangent is
+.IR x .
+.SH RETURN VALUE
+On success, these functions return the principal value of the arc tangent of
+.I x
+in radians; the return value is in the range [\-pi/2,\ pi/2].
+.P
+If
+.I x
+is a NaN, a NaN is returned.
+.P
+If
+.I x
+is +0 (\-0),
++0 (\-0) is returned.
+.P
+If
+.I x
+is positive infinity (negative infinity), +pi/2 (\-pi/2) is returned.
+.\"
+.\" POSIX.1-2001 documents an optional range error for subnormal x;
+.\" glibc 2.8 does not do this.
+.SH ERRORS
+No errors occur.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR atan (),
+.BR atanf (),
+.BR atanl ()
+T}	Thread safety	MT-Safe
+.TE
+.SH STANDARDS
+C11, POSIX.1-2008.
+.SH HISTORY
+C99, POSIX.1-2001.
+.P
+The variant returning
+.I double
+also conforms to
+SVr4, 4.3BSD, C89.
+.SH SEE ALSO
+.BR acos (3),
+.BR asin (3),
+.BR atan2 (3),
+.BR carg (3),
+.BR catan (3),
+.BR cos (3),
+.BR sin (3),
+.BR tan (3)