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docs: 4Q flux measurement operator design (square + tetra) - #32

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Jul 8, 2026
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docs: 4Q flux measurement operator design (square + tetra)#32
ThinkOffApp merged 2 commits into
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docs/4q-flux-spec

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Design spec for the 4Q flux operators, requested by Petrus 2026-07-08 ("design the quark flux measurement operators! for square and tetra") — the P4 physics of the accepted 4Q spec (#28), done as a Fable advisor pass per the model routing.

Core design:

  • Flux correlator matrix F_ij,P(r;T) over the SU(2)-complete pairing basis {A,B}, probe plaquette at the T/2 timeslice, per-site W_ij trace fields reused straight from the P2/P3 potential measurement — flux piggybacks on already-built sources.
  • State projection in postprocessing only: GEVP eigenvectors contract the raw matrix → ground state AND first excited state (pairing flip-flop map) from the same data; (T₀,T) becomes a stability check, not a burned-in choice.
  • All 6 plaquette plane classes stored in the source canonical frame (E/B decomposition, action/energy densities, Michael sum rules); frame mapping under tdir/orientation averaging is unit-tested round-trip.
  • Generic stabilizer engine for probe wedges + the mandatory |G|/|stab| weights (the 56% overcount trap): must reproduce the hand-verified square/tetra viewer wedges exactly; expected orders 16/8/16/24 asserted.
  • Same-config 2Q references (on-axis + diagonal — the diagonals-only production decision extends naturally here) → site-by-site Δf binding-rearrangement maps.
  • Raw (F, W̄, □̄) triplet storage; ensemble ratio + single vacuum subtraction in postprocessing (PR flux: measure probe plaquette on unsmeared field #12/flux: ensemble-level ratio estimator for connected correlator #13/flux: apply vacuum subtraction once, in postprocessing #14/docs: stop overselling resampling as multilevel/multihit #15 discipline). Sizes = PGM 9804004 even-d set. Hard-gated on the 24⁴ --device-mem census.
  • Phases F1 (stabilizer engine, pure python) → F2 (2Q box flux, continuity gate vs existing profiles) → F3 (square) → F4 (tetra, beyond published PGM).

§10 has five open questions for Petrus (size set, margin, T_flux, excited-state scope, tetra validation anchor).

🤖 Generated with Claude Code

Flux correlator matrix F_ij,P(r;T) with probe at T/2, GEVP-contracted in
postprocessing (ground + excited from the same raw data); all 6 plaquette
plane classes in the source canonical frame (E/B decomposition, sum rules);
probe boxes reduced by a generic stabilizer engine with |G|/|stab| weights
(orders: 2Q 16, diag-2Q 8, square 16, tetra 24 — asserted as unit tests,
must reproduce the hand-verified viewer wedges exactly); same-config 2Q
references (on-axis + diagonal) for site-by-site binding-rearrangement
maps; PGM 9804004 even-d size set; raw-triplet storage with ensemble-ratio
+ single vacuum subtraction in postprocessing; gated on the 24^4
device-mem census. Phased F1-F4 with parity/continuity/physics gates.

Tetra flux is beyond the published PGM program — flagged as such.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Comment thread docs/4q_flux_measurement_spec.md Outdated
…f re-centering

Codex found the section-7 site-set-equality-with-viewer gate is impossible
(probe box != viewer domain: viewer square hMax=5, tetra spherical cutoff,
vs my rectangular m=3 box). Verified directly against tools/geometry_viewer.html
and fixed, plus a 3-agent audit surfaced more:

- BLOCKING: Delta-f was defined center-relative-per-geometry, but a 2Q pair
  midpoint is offset from the 4Q center (d/2 for a square side) -> equal r
  subtracts different physical points. Now defined in ABSOLUTE coords with an
  unfold + re-center-to-pair-center step and a coincidence gate (s7 f).
- BLOCKING: s3 repeated the impossible site-set-equality (and self-contradicted
  Sweights==box-volume). Replaced with predicate/orbit checks on the box.
- s7 gate 1 rewritten (adversary-hardened): selector equivalence vs viewer
  predicates sqSymLevel/tetSymLevel/q2SymLevel on a common G-invariant domain
  (diagonal-2Q has no viewer predicate -> brute-force ref); orbit-COVER
  partition test (not a Sweights checksum) to actually exercise |stab| weights;
  wall-site + parity coverage requirement.
- s8 costs: were flat volume/|G| (undercount ~55-65%) and d=8 was arithmetically
  wrong (137). Replaced with EXACT orbit-representative counts computed by
  brute force: square 60/84/112/144, tetra 55/91, on-axis 2Q 50/60/70/80,
  diag 2Q 100/144/196/256; ~15.5k passes/tdir.
- Dropped the 'doubled coordinates' convention: false viewer-provenance
  (viewer is floor-centered, not doubled) and moot for even-d flux.
- diagonal 2Q extended to d=8 so the d=8 square B-pairing has a reference.
- nits: T_d->D4h square label; T0/T is eigenvector-side not flux sink T;
  frame map applied at measurement.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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@ThinkOffApp
ThinkOffApp merged commit 05151be into main Jul 8, 2026
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