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32 .\" @(#)atan2.3 8.1 (Berkeley) 6/4/93
40 .Nd arc tangent function of two variables
44 .Fn atan2 "double y" "double x"
48 function computes the principal value of the arc tangent of
50 using the signs of both arguments to determine the quadrant of
55 function, if successful,
56 returns the arc tangent of
60 .Bq \&- Ns \*(Pi , \&+ Ns \*(Pi
67 are zero, the global variable
73 .Bl -column atan_(y,x)_:=____ sign(y)_(Pi_atan2(Xy_xX))___
74 .It Fn atan2 y x No := Ta
79 .It Ta sign( Ns Ar y Ns )*(\*(Pi -
80 .Fn atan "\\*(Bay/x\\*(Ba" ) Ta
88 .Pf sign( Ar y Ns )*\\*(Pi/2 Ta
101 despite that previously
103 may have generated an error message.
104 The reasons for assigning a value to
107 .Bl -enum -offset indent
109 Programs that test arguments to avoid computing
111 must be indifferent to its value.
112 Programs that require it to be invalid are vulnerable
113 to diverse reactions to that invalidity on diverse computer systems.
117 function is used mostly to convert from rectangular (x,y)
123 coordinates that must satisfy x =
133 These equations are satisfied when (x=0,y=0)
139 on a VAX. In general, conversions to polar coordinates
140 should be computed thus:
141 .Bd -unfilled -offset indent
143 r := hypot(x,y); ... := sqrt(x\(**x+y\(**y)
147 r := hypot(x,y); ... := \(sr(x\u\s82\s10\d+y\u\s82\s10\d)
152 The foregoing formulas need not be altered to cope in a
153 reasonable way with signed zeros and infinities
154 on a machine that conforms to
161 such a machine are designed to handle all cases.
166 In general the formulas above are equivalent to these:
167 .Bd -unfilled -offset indent
169 r := sqrt(x\(**x+y\(**y); if r = 0 then x := copysign(1,x);
171 r := \(sr(x\(**x+y\(**y);\0\0if r = 0 then x := copysign(1,x);