[AlexKurek]

The original implementation computed the 4-quadrant position angle manually:

1. atan(abs(y / x)) calculated a reference angle in $[0, \pi/2]$.
2. atanproper mapped this angle into $[0, 2\pi)$ using conditional checks based on the signs of $x$ (m2[0] - m2[1]) and $y$ (2.0 * m11).

Replacing this with np.arctan2(y, x) % (2 * pi) is mathematically identical:

• np.arctan2(y, x) computes the 4-quadrant angle in $[-\pi, \pi]$.
• The % (2 * pi) modulo converts negative angles to $[0, 2\pi)$, matching the mapping of atanproper.

It prevents crashes when $x = 0$ (m2[0] == m2[1], as np.arctan2 handles zero denominators.

[gmloose]

I think it's safe to remove atanproper from bdsf/functions.py. I don't think it's being used outside PyBDSF, and this was the only place in this repository where it was used.

[AlexKurek]

It is also used in gdist_pa.

[gmloose]

It is also used in gdist_pa.

Any reason why you cannot use math.atan2 in that method?

[AlexKurek]

No, no reason, changed it.

[AlexKurek]

The test crashed, I got an email.