fix(math): correct comment-extremity sign in pca_project_cmnts (D1b)#2615
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fix(math): correct comment-extremity sign in pca_project_cmnts (D1b)#2615jucor wants to merge 1 commit into
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This was referenced Jul 17, 2026
`pca_project_cmnts` computed `coefs = -scale * (1.0 + center)`, a literal, untranslated copy of Clojure's synthetic vote value `-1` (pca.clj:167-178). Clojure stays in raw-Postgres convention (AGREE=-1) throughout, so `-1` is correct there. Delphi flips votes to its own convention at the Postgres ingress (`postgres_vote_to_delphi`), fitting PCA on AGREE=+1 data, so the untranslated `-1` INVERTS comment extremity: `|correct| = scale*|1-center|` vs `|actual| = scale*|1+center|` (equal only at center==0). A near-unanimous-AGREE comment (center -> +1) read as maximally extreme (2*scale) instead of ~0; a near-unanimous-DISAGREE comment (center -> -1) read as ~0 instead of maximal. Fix: `coefs = scale * (AGREE - center)` (AGREE=+1, from utils.general) — the faithful Delphi-convention port of Clojure's synthetic-AGREE projection. Docstring rewritten to document the convention translation. Tests (TDD, RED->GREEN): - Replace the tautological `test_pca_project_cmnts_formula` (it re-derived the implementation's own buggy formula) with one deriving expected values independently from the AGREE constant. - Add a behavioral sign test: unanimous-agree -> extremity 0, unanimous-disagree -> maximal. - Add an integration test spying on the extremity `E` reaching `priority_metric` through `_compute_comment_priorities` (works despite the #2571 mirror — it inspects the argument, not the return), pinned to hand-derived 0 and 2*sqrt(2). - Provenance comment in regression/utils.py: the regression CSVs are pre-flipped to Delphi convention by server/src/report.ts (~line 393, `String(-row.vote)`), so the regression path must NOT re-flip. Output-inert today: `priority_metric` still returns META_PRIORITY**2 (the #2571 Clojure bug-mirror), so extremity affects no DynamoDB output yet and no golden snapshots move. This is the extremity/PCA-parity groundwork the D12 `priority_metric` un-mirror is blocked on. Distinct from D1 (align_pca_signs, temporal ±eigenvector stability). Full delphi suite: 406 passed / 17 skipped / 47 xfailed / 0 failed. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> commit-id:a6494735
This was referenced Jul 18, 2026
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This was referenced Jul 18, 2026
Delphi Coverage Report
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pca_project_cmntscomputedcoefs = -scale * (1.0 + center), a literal,untranslated copy of Clojure's synthetic vote value
-1(pca.clj:167-178).Clojure stays in raw-Postgres convention (AGREE=-1) throughout, so
-1iscorrect there. Delphi flips votes to its own convention at the Postgres ingress
(
postgres_vote_to_delphi), fitting PCA on AGREE=+1 data, so the untranslated-1INVERTS comment extremity:|correct| = scale*|1-center|vs|actual| = scale*|1+center|(equal only at center==0). A near-unanimous-AGREEcomment (center -> +1) read as maximally extreme (2*scale) instead of ~0; a
near-unanimous-DISAGREE comment (center -> -1) read as ~0 instead of maximal.
Fix:
coefs = scale * (AGREE - center)(AGREE=+1, from utils.general) — thefaithful Delphi-convention port of Clojure's synthetic-AGREE projection.
Docstring rewritten to document the convention translation.
Tests (TDD, RED->GREEN):
test_pca_project_cmnts_formula(it re-derived theimplementation's own buggy formula) with one deriving expected values
independently from the AGREE constant.
unanimous-disagree -> maximal.
Ereachingpriority_metricthrough
_compute_comment_priorities(works despite the Clojure math.repness: priority-metric meta detection treats 0 as truthy, assigning META_PRIORITY^2 to every comment #2571 mirror — itinspects the argument, not the return), pinned to hand-derived 0 and 2*sqrt(2).
to Delphi convention by server/src/report.ts (~line 393,
String(-row.vote)),so the regression path must NOT re-flip.
Output-inert today:
priority_metricstill returns META_PRIORITY**2 (the #2571Clojure bug-mirror), so extremity affects no DynamoDB output yet and no golden
snapshots move. This is the extremity/PCA-parity groundwork the D12
priority_metricun-mirror is blocked on. Distinct from D1 (align_pca_signs,temporal ±eigenvector stability).
Full delphi suite: 406 passed / 17 skipped / 47 xfailed / 0 failed.
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com
commit-id:a6494735
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