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>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .\" References consulted:
   8 .\"     Linux libc source code
   9 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  10 .\"     386BSD man pages
  11 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  12 .\" Modified 2002-07-27 by Walter Harms
  13 .\"     (walter.harms@informatik.uni-oldenburg.de)
  14 .\"
  15 .TH ATAN2 3 2021-03-22 GNU "Linux Programmer's Manual"
  16 .SH NAME
  17 atan2, atan2f, atan2l \- arc tangent function of two variables
  18 .SH LIBRARY
  19 Math library
  20 .RI ( libm ", " \-lm )
  21 .SH SYNOPSIS
  22 .nf
  23 .B #include <math.h>
  24 .PP
  25 .BI "double atan2(double " y ", double " x );
  26 .BI "float atan2f(float " y ", float " x );
  27 .BI "long double atan2l(long double " y ", long double " x );
  28 .fi
  29 .PP
  30 .RS -4
  31 Feature Test Macro Requirements for glibc (see
  32 .BR feature_test_macros (7)):
  33 .RE
  34 .PP
  35 .BR atan2f (),
  36 .BR atan2l ():
  37 .nf
  38     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  39         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  40         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  41 .fi
  42 .SH DESCRIPTION
  43 These functions calculate the principal value of the arc tangent of
  44 .IR y/x ,
  45 using the signs of the two arguments to determine
  46 the quadrant of the result.
  47 .SH RETURN VALUE
  48 On success, these functions return the principal value of the arc tangent of
  49 .I y/x
  50 in radians; the return value is in the range [\-pi,\ pi].
  51 .PP
  52 If
  53 .I y
  54 is +0 (\-0) and
  55 .I x
  56 is less than 0, +pi (\-pi) is returned.
  57 .PP
  58 If
  59 .I y
  60 is +0 (\-0) and
  61 .I x
  62 is greater than 0, +0 (\-0) is returned.
  63 .PP
  64 If
  65 .I y
  66 is less than 0 and
  67 .I x
  68 is +0 or \-0, \-pi/2 is returned.
  69 .PP
  70 If
  71 .I y
  72 is greater than 0 and
  73 .I x
  74 is +0 or \-0, pi/2 is returned.
  75 .PP
  76 .\" POSIX.1 says:
  77 .\" If
  78 .\" .I x
  79 .\" is 0, a pole error shall not occur.
  80 .\"
  81 If either
  82 .I x
  83 or
  84 .I y
  85 is NaN, a NaN is returned.
  86 .PP
  87 .\" POSIX.1 says:
  88 .\" If the result underflows, a range error may occur and
  89 .\" .I y/x
  90 .\" should be returned.
  91 .\"
  92 If
  93 .I y
  94 is +0 (\-0) and
  95 .I x
  96 is \-0, +pi (\-pi) is returned.
  97 .PP
  98 If
  99 .I y
 100 is +0 (\-0) and
 101 .I x
 102 is +0, +0 (\-0) is returned.
 103 .PP
 104 If
 105 .I y
 106 is a finite value greater (less) than 0, and
 107 .I x
 108 is negative infinity, +pi (\-pi) is returned.
 109 .PP
 110 If
 111 .I y
 112 is a finite value greater (less) than 0, and
 113 .I x
 114 is positive infinity, +0 (\-0) is returned.
 115 .PP
 116 If
 117 .I y
 118 is positive infinity (negative infinity), and
 119 .I x
 120 is finite,
 121 pi/2 (\-pi/2) is returned.
 122 .PP
 123 If
 124 .I y
 125 is positive infinity (negative infinity) and
 126 .I x
 127 is negative infinity, +3*pi/4 (\-3*pi/4) is returned.
 128 .PP
 129 If
 130 .I y
 131 is positive infinity (negative infinity) and
 132 .I x
 133 is positive infinity, +pi/4 (\-pi/4) is returned.
 134 .\"
 135 .\" POSIX.1 says:
 136 .\" If both arguments are 0, a domain error shall not occur.
 137 .SH ERRORS
 138 No errors occur.
 139 .\" POSIX.1 documents an optional underflow error
 140 .\" glibc 2.8 does not do this.
 141 .SH ATTRIBUTES
 142 For an explanation of the terms used in this section, see
 143 .BR attributes (7).
 144 .ad l
 145 .nh
 146 .TS
 147 allbox;
 148 lbx lb lb
 149 l l l.
 150 Interface       Attribute       Value
 151 T{
 152 .BR atan2 (),
 153 .BR atan2f (),
 154 .BR atan2l ()
 155 T}      Thread safety   MT-Safe
 156 .TE
 157 .hy
 158 .ad
 159 .sp 1
 160 .SH CONFORMING TO
 161 C99, POSIX.1-2001, POSIX.1-2008.
 162 .PP
 163 The variant returning
 164 .I double
 165 also conforms to
 166 SVr4, 4.3BSD, C89.
 167 .SH SEE ALSO
 168 .BR acos (3),
 169 .BR asin (3),
 170 .BR atan (3),
 171 .BR carg (3),
 172 .BR cos (3),
 173 .BR sin (3),
 174 .BR tan (3)