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  12 .TH atan2 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions"
  13 .SH NAME
  14 atan2, atan2f, atan2l \- arc tangent function
  15 .SH SYNOPSIS
  16 .LP
  17 .nf
  18 c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
  19 #include <math.h>
  20 
  21 \fBdouble\fR \fBatan2\fR(\fBdouble\fR \fIy\fR, \fBdouble\fR \fIx\fR);
  22 .fi
  23 
  24 .LP
  25 .nf
  26 \fBfloat\fR \fBatan2f\fR(\fBfloat\fR \fIy\fR, \fBfloat\fR \fIx\fR);
  27 .fi
  28 
  29 .LP
  30 .nf
  31 \fBlong double\fR \fBatan2l\fR(\fBlong double\fR \fIy\fR, \fBlong double\fR \fIx\fR);
  32 .fi
  33 
  34 .SH DESCRIPTION
  35 .sp
  36 .LP
  37 These functions compute the principal value of the arc tangent of \fIy/x\fR,
  38 using the signs of both arguments to determine the quadrant of the return
  39 value.
  40 .SH RETURN VALUES
  41 .sp
  42 .LP
  43 Upon successful completion, these functions return the arc tangent of
  44 \fIy\fR/\fIx\fR in the range [ \(mi\c
  45 .if n pi\c
  46 .if t \(*p
  47 \c
  48 ,\c
  49 .if n pi\c
  50 .if t \(*p
  51 \c
  52  ] radians.
  53 .sp
  54 .LP
  55 If \fIy\fR is \(+-0 and \fIx\fR is < 0, \(+-\c
  56 .if n pi\c
  57 .if t \(*p
  58 \c
  59  is returned.
  60 .sp
  61 .LP
  62 If \fIy\fR is \(+-0 and \fIx\fR is > 0, \(+-0 is returned.
  63 .sp
  64 .LP
  65 If \fIy\fR is < 0 and \fIx\fR is \(+-0, \(mi\c
  66 .if n pi\c
  67 .if t \(*p
  68 \c
  69 /2 is returned.
  70 .sp
  71 .LP
  72 If \fIy\fR is > 0 and \fIx\fR is \(+-0, \c
  73 .if n pi\c
  74 .if t \(*p
  75 \c
  76 /2 is returned.
  77 .sp
  78 .LP
  79 If \fIx\fR is 0, a pole error does not occur.
  80 .sp
  81 .LP
  82 If either \fIx\fR or \fIy\fR is NaN, a NaN is returned.
  83 .sp
  84 .LP
  85 If \fIy\fR is \(+-0 and \fIx\fR is -0, \(+-\c
  86 .if n pi\c
  87 .if t \(*p
  88 \c
  89  is returned.
  90 .sp
  91 .LP
  92 If \fIy\fR is \(+-0 and \fIx\fR is +0, \(+-0 is returned.
  93 .sp
  94 .LP
  95 For finite values of \(+-\fIy\fR > 0, if x is \(miInf,  \(+-\c
  96 .if n pi\c
  97 .if t \(*p
  98 \c
  99  is returned.
 100 .sp
 101 .LP
 102 For finite values of \(+-\fIy\fR > 0, if x is +Inf,  \(+-0 is returned.
 103 .sp
 104 .LP
 105 For finite values of \fIx\fR, if \fIy\fR is \(+-Inf, \(+-\c
 106 .if n pi\c
 107 .if t \(*p
 108 \c
 109 /2 is returned.
 110 .sp
 111 .LP
 112 If \fIy\fR is \(+-Inf and \fIx\fR is \(miInf, \(+-3\c
 113 .if n pi\c
 114 .if t \(*p
 115 \c
 116 /4 is returned.
 117 .sp
 118 .LP
 119 If \fIy\fR is \(+-Inf and \fIx\fR is +Inf, \(+-\c
 120 .if n pi\c
 121 .if t \(*p
 122 \c
 123 /4 is returned.
 124 .sp
 125 .LP
 126 If both arguments are 0, a domain error does not occur.
 127 .SH ERRORS
 128 .sp
 129 .LP
 130 No errors are defined.
 131 .SH ATTRIBUTES
 132 .sp
 133 .LP
 134 See \fBattributes\fR(5) for descriptions of the following attributes:
 135 .sp
 136 
 137 .sp
 138 .TS
 139 tab() box;
 140 cw(2.75i) |cw(2.75i) 
 141 lw(2.75i) |lw(2.75i) 
 142 .
 143 ATTRIBUTE TYPEATTRIBUTE VALUE
 144 _
 145 Interface StabilityStandard
 146 _
 147 MT-LevelMT-Safe
 148 .TE
 149 
 150 .SH SEE ALSO
 151 .sp
 152 .LP
 153 \fBatan\fR(3M), \fBisnan\fR(3M), \fBmath.h\fR(3HEAD)\fBtan\fR(3M),
 154 \fBattributes\fR(5), \fBstandards\fR(5)