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Use arctan2 for calculating pert_motion_field as opposed to arctan #2

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Use arctan2 for calculating pert_motion_field as opposed to arctan #2

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e561c78
Switch to using np.arctan2 for Probabilistic Advection
KristianHMoller Jun 29, 2026
719da66
Add comment on the use of arctan2
KristianHMoller Jun 29, 2026
644ccbe
License added by repo owner
KristianHMoller Jul 1, 2026
6c5d52b
Add changelog
KristianHMoller Jul 8, 2026
ac9ff41
Merge branch 'dmidk:main' into bugfix/arctan
KristianHMoller Jul 8, 2026
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13 changes: 13 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
# Changelog

All notable changes to this project will be documented in this file.

The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

## [Unreleased]

### Fixed

- Switch to using np.arctan2 rather than np.arctan for Probabilistic Advection [#2](https://github.com/dmidk/SolarSTEPS/pull/2), @KristianHMoller

6 changes: 4 additions & 2 deletions Models/ProbabilisticAdvection.py
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Expand Up @@ -62,8 +62,10 @@ def ens_forecast(self,
else:
raise Exception('angle_pert_dist must be either normal or vonmises')

pert_motion_field[0, :, :] = pert_abs * np.cos(np.arctan(y / x) + beta_noise)
pert_motion_field[1, :, :] = pert_abs * np.sin(np.arctan(y / x) + beta_noise)
# Use arctan2 for angle calculation to handle all quadrants correctly
base_angle = np.arctan2(y, x)
pert_motion_field[0, :, :] = pert_abs * np.cos(base_angle + beta_noise)
pert_motion_field[1, :, :] = pert_abs * np.sin(base_angle + beta_noise)

yhat_maps = self.extrapolate(self.last_map,
pert_motion_field,
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