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atan2 (3)

atan2 (3) ( Solaris man: Библиотечные вызовы )

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atan2 (3) ( Русские man: Библиотечные вызовы )

atan2 (3) ( Linux man: Библиотечные вызовы )

atan2 (3) ( POSIX man: Библиотечные вызовы )

BSD mandoc

NAME



atan2

 
atan2f

 - arc tangent functions of two variables

LIBRARY

Lb libm

SYNOPSIS

#include <math.h>
double atan2 (double y double x);
float atan2f (float y float x);

DESCRIPTION

The atan2 ();
and the atan2f ();
functions compute the principal value of the arc tangent of Fa y/ Ns Ar x , using the signs of both arguments to determine the quadrant of the return value.

RETURN VALUES

The atan2 ();
and the atan2f ();
functions, if successful, return the arc tangent of Fa y/ Ns Ar x in the range -words Bq - Ns , + Ns radians. Here are some of the special cases:

Fn atan2 y x := Ta Fn atan y/x Ta if: x > 0,
Ta sign( y )*(: atan (\*(Bay/x\*(Ba ) Ta);
if x < 0,
Ta 0 Ta if x = y = 0, or
Ta sign( y )*\*(Pi/2 Ta if: x = 0 != y

NOTES

The function atan2 ();
defines "if x > 0," atan2 (0 0);
= 0 despite that previously atan2 (0 0);
may have generated an error message. The reasons for assigning a value to atan2 (0 0);
are these:

Programs that test arguments to avoid computing atan2 (0 0);
must be indifferent to its value. Programs that require it to be invalid are vulnerable to diverse reactions to that invalidity on diverse computer systems.
The atan2 ();
function is used mostly to convert from rectangular (x,y) to polar (r,theta) coordinates that must satisfy x = r*cos theta and y = r*sin theta. These equations are satisfied when (x=0,y=0) is mapped to (r=0,theta=0). In general, conversions to polar coordinates should be computed thus:
```
r       := hypot(x,y);  ... := sqrt(x*x+y*y)
theta   := atan2(y,x).
```
The foregoing formulas need not be altered to cope in a reasonable way with signed zeros and infinities on a machine that conforms to IEEE 754 the versions of hypot(3) and atan2 ();
provided for such a machine are designed to handle all cases. That is why atan2 (±0 -0);
= ± for instance. In general the formulas above are equivalent to these:
```
r := sqrt(x*x+y*y); if r = 0 then x := copysign(1,x);
```