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Multiple SED in ChromaticTransformation by absolute value of determinant #1349

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Merged
rmjarvis merged 4 commits into from
Feb 22, 2026
Merged

Multiple SED in ChromaticTransformation by absolute value of determinant #1349

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4927ec2
Multiple SED in ChromaticTransformation by absolute value of determinant
FedericoBerlfein Feb 19, 2026
407fb5a
Change absolute value inside function
FedericoBerlfein Feb 19, 2026
fe82e30
Merge branch 'main' into 1346-negative-flux-chromatictransformation
rmjarvis Feb 20, 2026
c9b5069
Test flux is correct if jacobian has negative determinant
FedericoBerlfein Feb 20, 2026
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4 changes: 2 additions & 2 deletions galsim/chromatic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1903,9 +1903,9 @@ def sed(self):
@np.vectorize
def detjac(w):
return np.linalg.det(np.asarray(self._jac(w)).reshape(2,2))
sed *= detjac
sed *= np.abs(detjac)
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@rmjarvis rmjarvis Feb 19, 2026

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This is not correct. abs needs to be inside the function. Note that detjac here is a function, not a number.

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@FedericoBerlfein FedericoBerlfein Feb 19, 2026

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Yes I didn't notice this at first. Moved inside the function.

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@sidneymau sidneymau Feb 20, 2026 •
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If we wanted to keep detjac as returning a signed number and to only apply the absolute value when doing the SED transformation, then the following should work

sed *= lambda w: np.abs(detjac(w))

Python could really do with better support for functional composition...

elif self._jac is not None:
sed *= np.linalg.det(np.asarray(self._jac).reshape(2,2))
sed *= np.abs(np.linalg.det(np.asarray(self._jac).reshape(2,2)))

return sed

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