man3/atan2.3

   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 ATAN2 3  2016-03-15 "" "Linux Programmer's Manual"
  36 .SH NAME
  37 atan2, atan2f, atan2l \- arc tangent function of two variables
  38 .SH SYNOPSIS
  39 .nf
  40 .B #include <math.h>
  41
  42 .BI "double atan2(double " y ", double " x );
  43 .BI "float atan2f(float " y ", float " x );
  44 .BI "long double atan2l(long double " y ", long double " x );
  45
  46 .fi
  47 Link with \fI\-lm\fP.
  48 .sp
  49 .in -4n
  50 Feature Test Macro Requirements for glibc (see
  51 .BR feature_test_macros (7)):
  52 .in
  53 .sp
  54 .ad l
  55 .BR atan2f (),
  56 .BR atan2l ():
  57 .RS
  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 y/x ,
  66 using the signs of the two arguments to determine
  67 the quadrant of the result.
  68 .SH RETURN VALUE
  69 On success, these functions return the principal value of the arc tangent of
  70 .IR y/x
  71 in radians; the return value is in the range [\-pi,\ pi].
  72
  73 If
  74 .I y
  75 is +0 (\-0) and
  76 .I x
  77 is less than 0, +pi (\-pi) is returned.
  78
  79 If
  80 .I y
  81 is +0 (\-0) and
  82 .I x
  83 is greater than 0, +0 (\-0) is returned.
  84
  85 If
  86 .I y
  87 is less than 0 and
  88 .I x
  89 is +0 or \-0, \-pi/2 is returned.
  90
  91 If
  92 .I y
  93 is greater than 0 and
  94 .I x
  95 is +0 or \-0, pi/2 is returned.
  96
  97 .\" POSIX.1 says:
  98 .\" If
  99 .\" .I x
 100 .\" is 0, a pole error shall not occur.
 101 .\"
 102 If either
 103 .I x
 104 or
 105 .I y
 106 is NaN, a NaN is returned.
 107
 108 .\" POSIX.1 says:
 109 .\" If the result underflows, a range error may occur and
 110 .\" .I y/x
 111 .\" should be returned.
 112 .\"
 113 If
 114 .I y
 115 is +0 (\-0) and
 116 .I x
 117 is \-0, +pi (\-pi) is returned.
 118
 119 If
 120 .I y
 121 is +0 (\-0) and
 122 .I x
 123 is +0, +0 (\-0) is returned.
 124
 125 If
 126 .I y
 127 is a finite value greater (less) than 0, and
 128 .I x
 129 is negative infinity, +pi (\-pi) is returned.
 130
 131 If
 132 .I y
 133 is a finite value greater (less) than 0, and
 134 .I x
 135 is positive infinity, +0 (\-0) is returned.
 136
 137 If
 138 .I y
 139 is positive infinity (negative infinity), and
 140 .I x
 141 is finite,
 142 pi/2 (\-pi/2) is returned.
 143
 144 If
 145 .I y
 146 is positive infinity (negative infinity) and
 147 .I x
 148 is negative infinity, +3*pi/4 (\-3*pi/4) is returned.
 149
 150 If
 151 .I y
 152 is positive infinity (negative infinity) and
 153 .I x
 154 is positive infinity, +pi/4 (\-pi/4) is returned.
 155 .\"
 156 .\" POSIX.1 says:
 157 .\" If both arguments are 0, a domain error shall not occur.
 158 .SH ERRORS
 159 No errors occur.
 160 .\" POSIX.1 documents an optional underflow error
 161 .\" glibc 2.8 does not do this.
 162 .SH ATTRIBUTES
 163 For an explanation of the terms used in this section, see
 164 .BR attributes (7).
 165 .TS
 166 allbox;
 167 lbw28 lb lb
 168 l l l.
 169 Interface       Attribute       Value
 170 T{
 171 .BR atan2 (),
 172 .BR atan2f (),
 173 .BR atan2l ()
 174 T}      Thread safety   MT-Safe
 175 .TE
 176 .SH CONFORMING TO
 177 C99, POSIX.1-2001, POSIX.1-2008.
 178
 179 The variant returning
 180 .I double
 181 also conforms to
 182 SVr4, 4.3BSD, C89.
 183 .SH SEE ALSO
 184 .BR acos (3),
 185 .BR asin (3),
 186 .BR atan (3),
 187 .BR carg (3),
 188 .BR cos (3),
 189 .BR sin (3),
 190 .BR tan (3)