python-math #27: feat(delphi): Q12 carve-out — pin the cold-tick PCA start to ones in both replay drivers - #2655
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python-math #27: feat(delphi): Q12 carve-out — pin the cold-tick PCA start to ones in both replay drivers#2655jucor wants to merge 1 commit into
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This was referenced Jul 22, 2026
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python-math #43: docs(delphi): s7 goal state + journal — mode collapse executed, battery 20/20
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…start to ones in both replay drivers ## Why Quirk Q12: production Clojure draws an UNSEEDED random start vector for PCA power iteration on the cold tick — a conversation's first math update, where there is no previous result to warm-start from (`rand-starting-vec`, `pca.clj:79-82`, complete with the original author's own comment: "should really throw a [seeded] random number generator in the equation here... XXX"). With a small eigengap, the fixed 100 power iterations do not fully converge, so a start-dependent residual survives into the output (~4e-4 on the `pc-smallmix-01` battery entry at step 0). Even two Clojure runs differ on cold ticks — no deterministic reference exists to certify against. ## What Both replay drivers (the Clojure and Python harness programs that feed a recorded vote schedule through their respective engines) now pin the cold start to the ONES vector — the exact value power iteration already pads new-comment columns with (`pca.clj:46-49` / `pca.py` `_power_iteration`). The pin works by seeding the conversation with a single-element `[1.0]` start vector that the existing padding expands to any width (`dev/replay.clj` `certify-cold-start-pca`; `polismath/replay/driver.py`). Warm ticks are untouched: from tick 2 on they take the real previous components exactly as before. The pin is logged per run, and the quirk is ledgered as Q12 in `CLOJURE_QUIRKS.md`. ## Battery effect In the certification battery (recorded real-conversation vote schedules replayed through both engines and compared step by step): - `pc-smallmix-01` and `pc-midmix-01` went DIVERGENCE -> MATCH. - `pc-revote-01`'s step 0 cleared (its remaining residual from step 1 on comes from split-loop extraction order on tie-dense 15-comment geometry, diagnosed separately). - 14/15 MATCH with the five prodclone extractions (datasets extracted from the production-database clone) in the battery. commit-id:6b40e1bf
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Why
Quirk Q12: production Clojure draws an UNSEEDED random start vector for PCA power iteration on the cold tick — a conversation's first math update, where there is no previous result to warm-start from (
rand-starting-vec,pca.clj:79-82, complete with the original author's own comment: "should really throw a [seeded] random number generator in the equation here... XXX"). With a small eigengap, the fixed 100 power iterations do not fully converge, so a start-dependent residual survives into the output (~4e-4 on thepc-smallmix-01battery entry at step 0). Even two Clojure runs differ on cold ticks — no deterministic reference exists to certify against.What
Both replay drivers (the Clojure and Python harness programs that feed a recorded vote schedule through their respective engines) now pin the cold start to the ONES vector — the exact value power iteration already pads new-comment columns with (
pca.clj:46-49/pca.py_power_iteration). The pin works by seeding the conversation with a single-element[1.0]start vector that the existing padding expands to any width (dev/replay.cljcertify-cold-start-pca;polismath/replay/driver.py). Warm ticks are untouched: from tick 2 on they take the real previous components exactly as before. The pin is logged per run, and the quirk is ledgered as Q12 inCLOJURE_QUIRKS.md.Battery effect
In the certification battery (recorded real-conversation vote schedules replayed through both engines and compared step by step):
pc-smallmix-01andpc-midmix-01went DIVERGENCE -> MATCH.pc-revote-01's step 0 cleared (its remaining residual from step 1 on comes from split-loop extraction order on tie-dense 15-comment geometry, diagnosed separately).commit-id:6b40e1bf
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