atan2, atan2f, atan2l - arc tangent function
c99 [ flag... ] file... –lm [ library... ] #include <math.h> double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
These functions compute the principal value of the arc tangent of y/x, using the signs of both arguments to determine the quadrant of the return value.
Upon successful completion, these functions return the arc tangent of y/x in the range [ −π,π ] radians.
If y is ±0 and x is < 0, ±π is returned.
If y is ±0 and x is > 0, ±0 is returned.
If y is < 0 and x is ±0, −π/2 is returned.
If y is > 0 and x is ±0, π/2 is returned.
If x is 0, a pole error does not occur.
If either x or y is NaN, a NaN is returned.
If y is ±0 and x is –0, ±π is returned.
If y is ±0 and x is +0, ±0 is returned.
For finite values of ±y > 0, if x is −Inf, ±π is returned.
For finite values of ±y > 0, if x is +Inf, ±0 is returned.
For finite values of x, if y is ±Inf, ±π/2 is returned.
If y is ±Inf and x is −Inf, ±3π/4 is returned.
If y is ±Inf and x is +Inf, ±π/4 is returned.
If both arguments are 0, a domain error does not occur.
No errors are defined.
See attributes(5) for descriptions of the following attributes:
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atan(3M), isnan(3M), math.h(3HEAD)tan(3M), attributes(5), standards(5)