man3/atan.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
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  27 .\" References consulted:
  28 .\"     Linux libc source code
  29 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  30 .\"     386BSD man pages
  31 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  32 .\" Modified 2002-07-27 by Walter Harms
  33 .\"     (walter.harms@informatik.uni-oldenburg.de)
  34 .\"
  35 .TH ATAN 3  2016-03-15 "" "Linux Programmer's Manual"
  36 .SH NAME
  37 atan, atanf, atanl \- arc tangent function
  38 .SH SYNOPSIS
  39 .nf
  40 .B #include <math.h>
  41 .sp
  42 .BI "double atan(double " x );
  43 .br
  44 .BI "float atanf(float " x );
  45 .br
  46 .BI "long double atanl( long double " x );
  47 .sp
  48 .fi
  49 Link with \fI\-lm\fP.
  50 .sp
  51 .in -4n
  52 Feature Test Macro Requirements for glibc (see
  53 .BR feature_test_macros (7)):
  54 .in
  55 .sp
  56 .ad l
  57 .BR atanf (),
  58 .BR atanl ():
  59 .RS 4
  60 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  61     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  62     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  63 .RE
  64 .ad b
  65 .SH DESCRIPTION
  66 These functions calculate the principal value of the arc tangent of
  67 .IR x ;
  68 that is the value whose tangent is
  69 .IR x .
  70 .SH RETURN VALUE
  71 On success, these functions return the principal value of the arc tangent of
  72 .IR x
  73 in radians; the return value is in the range [\-pi/2,\ pi/2].
  74
  75 If
  76 .I x
  77 is a NaN, a NaN is returned.
  78
  79 If
  80 .I x
  81 is +0 (\-0),
  82 +0 (\-0) is returned.
  83
  84 If
  85 .I x
  86 is positive infinity (negative infinity), +pi/2 (\-pi/2) is returned.
  87 .\"
  88 .\" POSIX.1-2001 documents an optional range error for subnormal x;
  89 .\" glibc 2.8 does not do this.
  90 .SH ERRORS
  91 No errors occur.
  92 .SH ATTRIBUTES
  93 For an explanation of the terms used in this section, see
  94 .BR attributes (7).
  95 .TS
  96 allbox;
  97 lbw24 lb lb
  98 l l l.
  99 Interface       Attribute       Value
 100 T{
 101 .BR atan (),
 102 .BR atanf (),
 103 .BR atanl ()
 104 T}      Thread safety   MT-Safe
 105 .TE
 106 .SH CONFORMING TO
 107 C99, POSIX.1-2001, POSIX.1-2008.
 108
 109 The variant returning
 110 .I double
 111 also conforms to
 112 SVr4, 4.3BSD, C89.
 113 .SH SEE ALSO
 114 .BR acos (3),
 115 .BR asin (3),
 116 .BR atan2 (3),
 117 .BR carg (3),
 118 .BR catan (3),
 119 .BR cos (3),
 120 .BR sin (3),
 121 .BR tan (3)