)

A variant of atan.

Converts both arguments to doubles.

Returns the angle between the positive x-axis and the vector (`b`

,`a`

).
The result, in radians, is in the range -PI..PI.

If `b`

is positive, this is the same as `atan(b/a)`

.

The result is negative when `a`

is negative (including when `a`

is the
double -0.0).

If `a`

is equal to zero, the vector (`b`

,`a`

) is considered parallel to
the x-axis, even if `b`

is also equal to zero. The sign of `b`

determines
the direction of the vector along the x-axis.

Returns NaN if either argument is NaN.

## Source

```
/**
* A variant of [atan].
*
* Converts both arguments to doubles.
*
* Returns the angle between the positive x-axis and the vector ([b],[a]).
* The result, in radians, is in the range -PI..PI.
*
* If [b] is positive, this is the same as [:atan(b/a):].
*
* The result is negative when [a] is negative (including when [a] is the
* double -0.0).
*
* If [a] is equal to zero, the vector ([b],[a]) is considered parallel to
* the x-axis, even if [b] is also equal to zero. The sign of [b] determines
* the direction of the vector along the x-axis.
*
* Returns NaN if either argument is NaN.
*/
external double atan2(num a, num b);
```