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  2015-03-02 "" "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 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  59 _POSIX_C_SOURCE\ >=\ 200112L;
  60 .br
  61 or
  62 .I cc\ -std=c99
  63 .RE
  64 .ad b
  65 .SH DESCRIPTION
  66 These functions calculate the principal value of the arc tangent of
  67 .IR y/x ,
  68 using the signs of the two arguments to determine
  69 the quadrant of the result.
  70 .SH RETURN VALUE
  71 On success, these functions return the principal value of the arc tangent of
  72 .IR y/x
  73 in radians; the return value is in the range [\-pi,\ pi].
  74
  75 If
  76 .I y
  77 is +0 (\-0) and
  78 .I x
  79 is less than 0, +pi (\-pi) is returned.
  80
  81 If
  82 .I y
  83 is +0 (\-0) and
  84 .I x
  85 is greater than 0, +0 (\-0) is returned.
  86
  87 If
  88 .I y
  89 is less than 0 and
  90 .I x
  91 is +0 or \-0, \-pi/2 is returned.
  92
  93 If
  94 .I y
  95 is greater than 0 and
  96 .I x
  97 is +0 or \-0, pi/2 is returned.
  98
  99 .\" POSIX.1 says:
 100 .\" If
 101 .\" .I x
 102 .\" is 0, a pole error shall not occur.
 103 .\"
 104 If either
 105 .I x
 106 or
 107 .I y
 108 is NaN, a NaN is returned.
 109
 110 .\" POSIX.1 says:
 111 .\" If the result underflows, a range error may occur and
 112 .\" .I y/x
 113 .\" should be returned.
 114 .\"
 115 If
 116 .I y
 117 is +0 (\-0) and
 118 .I x
 119 is \-0, +pi (\-pi) is returned.
 120
 121 If
 122 .I y
 123 is +0 (\-0) and
 124 .I x
 125 is +0, +0 (\-0) is returned.
 126
 127 If
 128 .I y
 129 is a finite value greater (less) than 0, and
 130 .I x
 131 is negative infinity, +pi (\-pi) is returned.
 132
 133 If
 134 .I y
 135 is a finite value greater (less) than 0, and
 136 .I x
 137 is positive infinity, +0 (\-0) is returned.
 138
 139 If
 140 .I y
 141 is positive infinity (negative infinity), and
 142 .I x
 143 is finite,
 144 pi/2 (\-pi/2) is returned.
 145
 146 If
 147 .I y
 148 is positive infinity (negative infinity) and
 149 .I x
 150 is negative infinity, +3*pi/4 (\-3*pi/4) is returned.
 151
 152 If
 153 .I y
 154 is positive infinity (negative infinity) and
 155 .I x
 156 is positive infinity, +pi/4 (\-pi/4) is returned.
 157 .\"
 158 .\" POSIX.1 says:
 159 .\" If both arguments are 0, a domain error shall not occur.
 160 .SH ERRORS
 161 No errors occur.
 162 .\" POSIX.1 documents an optional underflow error
 163 .\" glibc 2.8 does not do this.
 164 .SH ATTRIBUTES
 165 For an explanation of the terms used in this section, see
 166 .BR attributes (7).
 167 .TS
 168 allbox;
 169 lbw28 lb lb
 170 l l l.
 171 Interface       Attribute       Value
 172 T{
 173 .BR atan2 (),
 174 .BR atan2f (),
 175 .BR atan2l ()
 176 T}      Thread safety   MT-Safe
 177 .TE
 178 .SH CONFORMING TO
 179 C99, POSIX.1-2001, POSIX.1-2008.
 180
 181 The variant returning
 182 .I double
 183 also conforms to
 184 SVr4, 4.3BSD, C89.
 185 .SH SEE ALSO
 186 .BR acos (3),
 187 .BR asin (3),
 188 .BR atan (3),
 189 .BR carg (3),
 190 .BR cos (3),
 191 .BR sin (3),
 192 .BR tan (3)