[Jammy2211]

Summary

Phase 5a of #638 (community proposal by @HRSAstro, PyAutoLabs/.github#39). The matrix-free interferometer utilities merged in phases 1–4 (#645, #650, #651, #652) are now selectable from a fit: InversionInterferometerMatrixFree, returned by the inversion factory when Settings(interferometer_route="matrix_free") is set on a dataset with a sparse operator. It never forms the dense (S, S) curvature or regularization matrices: PCG with the Powell preconditioner (or the primal-dual interior point with the positive-only solver), ln det(F + H) by stochastic Lanczos quadrature, ln det H exact from MaternSparse. PyAutoGalaxy's FitInterferometer reaches it through Settings with no other change (companion test PR in PyAutoGalaxy).

Closes #657.

Decisions taken (flagged for review):

• Over-sampling and a non-trivial primary beam are supported, not rejected as the prompt listed. The sparse mapping matrix is built from the parent's triplets, which already fold in sub_fraction and the beam; both cases match the FFT route to ~1e-11 in the new tests. Reverting to a raise is a few lines in _check_preconditions.
• The positive-only solver with use_edge_zeroed_pixels=True raises: the matrix-free interior point solves the full system and has no held-pixel set. With the packaged defaults (both flags on) Settings(interferometer_route="matrix_free") alone therefore raises; users pass use_edge_zeroed_pixels=False (or use_positive_only_solver=False). The phase-5c workspace example must say so.
• Only MaternSparse is accepted (the SLQ probes need its sparse factor); other regularizations raise rather than densify.

API Changes

• Settings(interferometer_route=...) accepts "matrix_free" beside None / "fft" / "numba"; packaged default unchanged (null).
• New aa.InversionInterferometerMatrixFree (subclass of InversionInterferometerSparse). Dense-only attributes (curvature_matrix, curvature_matrix_diag, curvature_reg_matrix, curvature_reg_matrix_reduced, reconstruction_covariance_matrix, reconstruction_noise_map, reconstruction_noise_map_with_covariance, reconstruction_noise_map_dict) raise InversionException.
• The factory raises InversionException for the route on a dataset without a sparse operator and for every configuration the class cannot represent; there is no silent fallback.
• inversion_plots skips the noise-map panel / CSV column when the inversion raises InversionException.
  See full details below.

Test Plan

• test_autoarray/inversion/inversion/interferometer/test_matrix_free.py (21 new): factory dispatch; reconstruction vs FFT route ~1.5e-11 relative; chi-squared, regularization term, ln det H ~1e-11; SLQ ln det(F+H) 0.10% from dense (documented tolerance 0.5%); positive-only parity; over-sampling and primary-beam parity; every unsupported configuration and dense attribute raises; Settings typo raises ValueError; JAX backend raises (importorskip).
• test_autoarray/inversion: 1088 passed, 4 xfailed; rest of test_autoarray: 1124 passed.
• PyAutoGalaxy companion branch: 90 interferometer tests pass against this branch (fit parity, positive-only, raises, visualizer).

Heart RED override (development only)

Heart was RED at launch and at ship. The live human authorized the override for this task on 2026-10-26 ("I approve of the overrider", then "approve" on the plan naming issue #657). Exact RED reasons at launch: release validation FAILED (stage integrate); PyAutoHeart/workflows/Release Integrate: failure; PyAutoHeart/workflows/Workspace Smoke: failure; manifest_drift/checks/workspace checkouts (manifest ↔ disk): red; Release readiness: release validation FAILED (stage integrate); autolens: red; Workspace validation: NOT ready — 1429p / 1f / 125s @ cloud#40294511523; test_run: red; Release validation: NOT release_ready — v? profile=? (2026-10-26T07:48:52+00:00); validation_report/stages/integrate: fail; PyAutoBrain: red; PyAutoLens: red; autolens_profiling: red; Worktree drift: 1 orphan / 0 missing / 3 dirty. Branch gates passed: PyAutoArray full test suite (above), black. No release, no merge through RED: merge needs its own human /prm with green required checks.

Full API Changes (for automation & release notes)

Removed

• None

Added

• autoarray.InversionInterferometerMatrixFree(dataset, linear_obj_list, settings=, xp=np, preloads=) — matrix-free interferometer inversion (NumPy/scipy only; one RectangularUniform mapper with MaternSparse; no linear function lists). Provides reconstruction, regularization_term, fast_chi_squared, log_det_curvature_reg_matrix_term (SLQ), log_det_regularization_matrix_term, the mapped-data dictionaries, and operator / regularization_matrix_sparse / regularization_factor_sparse / positive_result diagnostics.
• Settings(interferometer_route="matrix_free") — selects the class; documented in settings.py and config/general.yaml.

Migration

• None required; opt-in only. To use: aa.Settings(interferometer_route="matrix_free", use_edge_zeroed_pixels=False) with a RectangularUniform mesh and aa.reg.MaternSparse on a dataset after apply_sparse_operator(...).

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