fix: ConstantZeroth regularization is dead code (eye(P) shape bug + missing neighbors_sizes) #448

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1. Jammy2211 commented on Aug 18, 2026

   

   Jammy2211

   on Aug 18, 2026 – with Claude

   CollaboratorAuthor

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   Reproduced both defects on clean main (commit 7d1906e, 2026-08-18, numpy path, Python 3.12) before touching any code.

   Defect 2 — class API omits neighbors_sizes (fails first, masking defect 1):

   reg = aa.reg.ConstantZeroth(coefficient_neighbor=1.0, coefficient_zeroth=2.0)
   reg.regularization_matrix_from(linear_obj=mapper)  # 3x3 rectangular MockMapper

   Traceback (most recent call last):
     File "repro_448.py", line 31, in <module>
       reg.regularization_matrix_from(linear_obj=mapper)
     File "autoarray/inversion/regularization/constant_zeroth.py", line 121, in regularization_matrix_from
       return constant_zeroth_regularization_matrix_from(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   TypeError: constant_zeroth_regularization_matrix_from() missing 1 required positional argument: 'neighbors_sizes'
   

   Defect 1 — eye(P) shape bug in the util function (called directly with correct args; neighbors.shape = (9, 4), so S=9, P=4):

   constant_zeroth_regularization_matrix_from(
       coefficient=1.0, coefficient_zeroth=2.0,
       neighbors=np.asarray(mapper.neighbors),
       neighbors_sizes=np.asarray(mapper.neighbors.sizes),
   )

   Traceback (most recent call last):
     File "repro_448.py", line 45, in <module>
       mat = constant_zeroth_regularization_matrix_from(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     File "autoarray/inversion/regularization/constant_zeroth.py", line 73, in constant_zeroth_regularization_matrix_from
       return const + zeroth
              ~~~~~~^~~~~~~~
   ValueError: operands could not be broadcast together with shapes (9,9) (4,4)
   

   Sibling check: adapt_split_zeroth.py and brightness_zeroth.py do not carry the copy-paste pattern — their zeroth terms are built via xp.diag over per-pixel weights (brightness_zeroth_regularization_matrix_from), no eye(P) and no dropped argument. zeroth.py uses xp.eye(pixels) with pixels = linear_obj.params, which is the correct semantics constant_zeroth.py should have mirrored.

   Proceeding with the fix on feature/constant-zeroth-repair.

   ---

   Generated by Claude Code
2. Jammy2211 commented on Aug 18, 2026

   

   Jammy2211

   on Aug 18, 2026 – with Claude

   CollaboratorAuthor

   More actions

   Repair complete — PR #449 is up from feature/constant-zeroth-repair (commit 143ab43), closing this issue on merge.

   Done, in the issue's order:

   • Both failures reproduced on clean main first (tracebacks in the comment above).
   • Defect 1 fixed: zeroth term is now the full S x S scaled identity (xp.eye(S) * coefficient_zeroth**2), matching zeroth.py's semantics.
   • Defect 2 fixed: class API now threads neighbors_sizes=linear_obj.neighbors.sizes, mirroring Constant.
   • Siblings checked: adapt_split_zeroth.py / brightness_zeroth.py are clean of the pattern (diag-over-weights zeroth terms) — no changes there.
   • Tests added (numpy-only): shape (S, S) with S != P, no null mode (min eig >= lambda_z^2), reduction to Constant + lambda_z^2 * I, class-API smoke. All 4 pass.
   • Full pytest test_autoarray/: 988 passed, 59 skipped; 3 pre-existing environment failures (pynufft vs modern scipy's removed pinv2), identical on clean main, unrelated.

   Spectrum verification (9-pixel rectangular fixture, lambda_n = lambda_z = 1): Constant min eigenvalue 1e-8 (null mode on the jitter floor, condition number 6e8) → ConstantZeroth min eigenvalue 1.0 = lambda_z^2 (condition number 7). Exact element-wise + lambda_z^2 I shift relative to Constant. Full table in the PR body for Phase 8C to cite.

   Constraints honored: autoarray/__init__.py untouched, Constant/Adapt/AdaptSplit numerics untouched, nothing bundled, LF endings.

   Remaining: merge only — which stays with @Jammy2211.

   ---

   Generated by Claude Code
3. Jammy2211

   closed this as completedin #449on Aug 18, 2026