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| atan2 |
| Portability: | ISO/ANSI C conforming, UNIX compatible |
| SYNOPSIS | |
| DESCRIPTION | |
| RETURN VALUE | |
| DIAGNOSTICS | |
| EXAMPLE | |
| RELATED FUNCTIONS | |
| SEE ALSO |
| SYNOPSIS |
#include <math.h> double atan2(double y, double x);
| DESCRIPTION |
atan2
computes the angle defined by the positive x axis and a line through the point
(
x,y
) to the point (0, 0). The signs of
both values
x
and
y
are used to determine the quadrant of the result in a Cartesian system.
The result is the inverse trigonometric tangent of
y/x
if
x
is not 0.
| RETURN VALUE |
Provided that it is defined and computable,
the return value is the angular position of the point
x,y
. The return value is a double-precision, floating-point number
expressed in radians and lies in the half-open interval (-![[pi]](../common/images/pil.gif)
,)
. For input values (0.0,
y
), the return
value will be either /2 or -/2 if
y
does not equal 0.
| DIAGNOSTICS |
If both
x
and
y
are 0, an error message is
written to
stderr
and the function returns
0.0.
If an error occurs in
atan2
, the
_matherr
routine is called.
You can supply your own version of
_matherr
to suppress the diagnostic message or modify the value returned.
| EXAMPLE |
This example converts rectangular coordinates to polar coordinates:
#include <stdio.h>
#include <lcmath.h>
main()
{
double x, y; /* rectangular coordinates (x,y) */
double r, angle; /* polar coordinates (r,angle) */
puts("Enter the rectangular coordinates please: ");
scanf("%lf %lf", &x, &y );
r = sqrt((x*x) + (y*y));
/* Compute polar coordinates (radians). */
angle = atan2(y , x);
/* Convert radians to degrees. */
angle = (180.0 * angle)/M_PI;
printf("rect coords(%f,%f) -> polar coords(%f,%f)\n",
x,y,r,angle);
}
| RELATED FUNCTIONS |
| SEE ALSO |
|
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Copyright © 2001 by SAS Institute Inc., Cary, NC, USA. All rights reserved.