`gamma` enters only as `gamma * gamma`, so the sign was squared away:
measured against the old public-field form, `ConstantDrift(-0.0833)`
produced results bit identical to `ConstantDrift(0.0833)`. The sign was
neither rejected nor honoured — it vanished.
It could not be checked while the field was a public tuple position,
because there was nothing to intercept. Validating inside
`variance_for_elapsed` would have been worse: it runs in the sweep, so a
construction-time mistake would panic mid-inference, and `Gaussian::from_ms`
is a worked example of why that is the wrong place — rejecting NaN there
turned the NonFiniteResult reporting path into a crash.
So `ConstantDrift::new` is the only way in and it checks, with `gamma()`
to read the value back. 129 call sites rewritten across src, tests,
benches, examples and the README. The dated plan and spec documents under
docs/superpowers are left alone: they record what was built at the time,
and rewriting them would falsify that.
tests/constructor_validation.rs is the more valuable half. This defect
class was closed three times in one session and reopened twice, because
each fix validated the layer it had just touched and inferred the rest —
`HistoryBuilder`, then `Game`'s own entry points, then the constructors
beneath both. A per-site fix cannot notice the site nobody thought of, so
that file enumerates every public entry point taking a magnitude and
asserts each refuses negative and non-finite values.
It found an eleventh defect on its first run: `HistoryBuilder::score_sigma`
accepted infinity, because `inf > 0.0` is true and the assert only tested
positivity. Fixed, and its own `should_panic` message updated to match.
`Gaussian::from_ms` is deliberately exempt from the non-finite half, for
the reason above: a broken fit produces a NaN sigma legitimately and
`converge` must be allowed to report it.
The convergence-level drift-variance check stays and is now tested through
a custom `Drift` implementation, since `ConstantDrift` can no longer reach
it. That check is the only thing standing between a third-party `Drift`
and a NaN fit.
BREAKING CHANGE: `ConstantDrift`'s field is private. Replace
`ConstantDrift(x)` with `ConstantDrift::new(x)`, and `drift().0` with
`drift().gamma()`. `HistoryBuilder::score_sigma` now rejects infinity.
Closes#65
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011hcFjNDmHXZF8URGLku5zZ
`posterior_of` shipped in 0.5.0 reading a single slice. Measured against
a real Through-Time history that answers almost nothing: ustat's round
fit is 76 per-day slices whose last one holds a solo round, so 0 of 55
pair differences resolved and the single node that did was degenerate —
a one-competitor slice has no correlation to account for and returns the
marginal unchanged.
That was my mistake, and the fixture chose it. I validated against
single-slice histories, which is exactly the shape that cannot reveal
the problem. In a library whose premise is skill over time, competitors
are read at *their own* last appearance and those are different slices
by construction.
The joint is now time-expanded: one variable per appearance, linked by
the prior on a first appearance, the drift between consecutive ones, and
the within-slice event contrasts. Consecutive appearances with no drift
between them are the same variable rather than two joined by an infinite
precision, which keeps the matrix positive-definite when a competitor is
pinned with `drift_scale = 0`.
`posterior_of` now reads each competitor at their own latest appearance,
which is where `current_skill` reads them, so the two agree about which
posterior they describe. Adds `posterior_of_at(time, terms)` for a
comparison anchored to a moment, matching `learning_curve`'s reading.
Validated against a hand-written exact posterior for a two-competitor,
two-slice history — the precision matrix is spelled out in the test
rather than obtained from the crate, so it is an independent check
rather than a restatement. Also pinned: competitors last seen in
different slices now compare at all, means still agree with the
marginals, zero drift makes slice layout irrelevant, and more drift
widens a comparison across time.
BREAKING CHANGE: `posterior_of` and `expected_variance_reduction` now
consider the whole history rather than its latest slice, so results
change for any multi-slice history. `JointUnavailable` is now returned
when *any* slice holds ranked events, not just the last.
Refs #46, #47
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011hcFjNDmHXZF8URGLku5zZ
logaritmiskandClaude Opus 5