Merge pull request #1883 from pypeit/hotfix_cubevar

HOTFIX :: Datacube variance should be squared, not cubed
pypeit · Dec 19, 2024 · 016fc30 · 016fc30
2 parents 0cf0265 + 7dd9394
commit 016fc30
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diff --git a/doc/releases/1.17.2dev.rst b/doc/releases/1.17.2dev.rst
@@ -43,4 +43,5 @@ Bug Fixes
   in both spatial dimensions equal to half the field of view.
 - Fix the code for the extraction of the 1D flat spectrum, so that
   the spectrum is extracted even when `pixelflat_model` does not exist.
-
+- The variance cube previously had a cubic term, and this has been changed
+  to a quadratic term. This has been cross-checked with simple subpixel calculations.
diff --git a/pypeit/core/datacube.py b/pypeit/core/datacube.py
@@ -1822,7 +1822,7 @@ def subpixellate(output_wcs, bins, sciImg, ivarImg, waveImg, slitid_img_gpm, wgh
             vox_coord = vox_coord.reshape(numpix * num_all_subpixels, 3)
             # Use the "fast histogram" algorithm, that assumes regular bin spacing
             flxcube += histogramdd(vox_coord, bins=outshape, range=binrng, weights=np.repeat(this_sci[this_sl] * this_wght_subpix[this_sl], num_all_subpixels) * subpix_wght)
-            varcube += histogramdd(vox_coord, bins=outshape, range=binrng, weights=np.repeat(this_var[this_sl] * this_wght_subpix[this_sl]**2, num_all_subpixels) * subpix_wght**3)
+            varcube += histogramdd(vox_coord, bins=outshape, range=binrng, weights=np.repeat(this_var[this_sl] * this_wght_subpix[this_sl]**2, num_all_subpixels) * subpix_wght**2)  # NOTE :: This was changed from subpix_wght**3 to subpix_wght**2 by RJC on 2024-12-18
             normcube += histogramdd(vox_coord, bins=outshape, range=binrng, weights=np.repeat(this_wght_subpix[this_sl], num_all_subpixels) * subpix_wght)
 
     # Normalise the datacube and variance cube