numpy.arctan2(x1, x2, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj]) = <ufunc 'arctan2'>
Element-wise arc tangent of
x1/x2 choosing the quadrant correctly.
The quadrant (i.e., branch) is chosen so that
arctan2(x1, x2) is the signed angle in radians between the ray ending at the origin and passing through the point (1,0), and the ray ending at the origin and passing through the point (
x1). (Note the role reversal: the “
y-coordinate” is the first function parameter, the “
x-coordinate” is the second.) By IEEE convention, this function is defined for
x2 = +/-0 and for either or both of
x2 = +/-inf (see Notes for specific values).
This function is not defined for complex-valued arguments; for the so-called argument of complex values, use
arctan2 is identical to the
atan2 function of the underlying C library. The following special values are defined in the C standard: 
| || || |
|+/- 0||+0||+/- 0|
|+/- 0||-0||+/- pi|
|> 0||+/-inf||+0 / +pi|
|< 0||+/-inf||-0 / -pi|
Note that +0 and -0 are distinct floating point numbers, as are +inf and -inf.
|||ISO/IEC standard 9899:1999, “Programming language C.”|
Consider four points in different quadrants:
>>> x = np.array([-1, +1, +1, -1]) >>> y = np.array([-1, -1, +1, +1]) >>> np.arctan2(y, x) * 180 / np.pi array([-135., -45., 45., 135.])
Note the order of the parameters.
arctan2 is defined also when
x2 = 0 and at several other special points, obtaining values in the range
>>> np.arctan2([1., -1.], [0., 0.]) array([ 1.57079633, -1.57079633]) >>> np.arctan2([0., 0., np.inf], [+0., -0., np.inf]) array([ 0. , 3.14159265, 0.78539816])
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