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32 .\" @(#)atan2.3 8.1 (Berkeley) 6/4/93
33 .\" $FreeBSD: src/lib/libm/common_source/atan2.3,v 1.5.2.4 2001/07/22 12:07:16 dd Exp $
40 .Nd arc tangent function of two variables
46 .Fn atan2 "double y" "double x"
50 function computes the principal value of the arc tangent of
52 using the signs of both arguments to determine the quadrant of
57 function, if successful,
58 returns the arc tangent of
62 .Bq \&- Ns \*(Pi , \&+ Ns \*(Pi
69 are zero, the global variable
75 .Bl -column atan_(y,x)_:=____ sign(y)_(Pi_atan2(Xy_xX))___
76 .It Fn atan2 y x No := Ta
81 .It Ta sign( Ns Ar y Ns )*(\*(Pi -
82 .Fn atan "\\*(Bay/x\\*(Ba" ) Ta
90 .Pf sign( Ar y Ns )*\\*(Pi/2 Ta
103 despite that previously
105 may have generated an error message.
106 The reasons for assigning a value to
109 .Bl -enum -offset indent
111 Programs that test arguments to avoid computing
113 must be indifferent to its value.
114 Programs that require it to be invalid are vulnerable
115 to diverse reactions to that invalidity on diverse computer systems.
119 function is used mostly to convert from rectangular (x,y)
125 coordinates that must satisfy x =
135 These equations are satisfied when (x=0,y=0)
141 on a VAX. In general, conversions to polar coordinates
142 should be computed thus:
143 .Bd -unfilled -offset indent
145 r := hypot(x,y); ... := sqrt(x\(**x+y\(**y)
149 r := hypot(x,y); ... := \(sr(x\u\s82\s10\d+y\u\s82\s10\d)
154 The foregoing formulas need not be altered to cope in a
155 reasonable way with signed zeros and infinities
156 on a machine that conforms to
163 such a machine are designed to handle all cases.
168 In general the formulas above are equivalent to these:
169 .Bd -unfilled -offset indent
171 r := sqrt(x\(**x+y\(**y); if r = 0 then x := copysign(1,x);
173 r := \(sr(x\(**x+y\(**y);\0\0if r = 0 then x := copysign(1,x);