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  2017-09-15 "" "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 .PP
  42 .BI "double atan(double " x );
  43 .BI "float atanf(float " x );
  44 .BI "long double atanl( long double " x );
  45 .PP
  46 .fi
  47 Link with \fI\-lm\fP.
  48 .PP
  49 .in -4n
  50 Feature Test Macro Requirements for glibc (see
  51 .BR feature_test_macros (7)):
  52 .in
  53 .PP
  54 .ad l
  55 .BR atanf (),
  56 .BR atanl ():
  57 .RS 4
  58 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  59     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  60     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  61 .RE
  62 .ad b
  63 .SH DESCRIPTION
  64 These functions calculate the principal value of the arc tangent of
  65 .IR x ;
  66 that is the value whose tangent is
  67 .IR x .
  68 .SH RETURN VALUE
  69 On success, these functions return the principal value of the arc tangent of
  70 .IR x
  71 in radians; the return value is in the range [\-pi/2,\ pi/2].
  72 .PP
  73 If
  74 .I x
  75 is a NaN, a NaN is returned.
  76 .PP
  77 If
  78 .I x
  79 is +0 (\-0),
  80 +0 (\-0) is returned.
  81 .PP
  82 If
  83 .I x
  84 is positive infinity (negative infinity), +pi/2 (\-pi/2) is returned.
  85 .\"
  86 .\" POSIX.1-2001 documents an optional range error for subnormal x;
  87 .\" glibc 2.8 does not do this.
  88 .SH ERRORS
  89 No errors occur.
  90 .SH ATTRIBUTES
  91 For an explanation of the terms used in this section, see
  92 .BR attributes (7).
  93 .TS
  94 allbox;
  95 lbw24 lb lb
  96 l l l.
  97 Interface       Attribute       Value
  98 T{
  99 .BR atan (),
 100 .BR atanf (),
 101 .BR atanl ()
 102 T}      Thread safety   MT-Safe
 103 .TE
 104 .SH CONFORMING TO
 105 C99, POSIX.1-2001, POSIX.1-2008.
 106 .PP
 107 The variant returning
 108 .I double
 109 also conforms to
 110 SVr4, 4.3BSD, C89.
 111 .SH SEE ALSO
 112 .BR acos (3),
 113 .BR asin (3),
 114 .BR atan2 (3),
 115 .BR carg (3),
 116 .BR catan (3),
 117 .BR cos (3),
 118 .BR sin (3),
 119 .BR tan (3)