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ashvale-station/tests
kemal e3176e29c9 Stride training pairs by the horizon instead of by the grid row
fit() trained every head on every consecutive grid row. At the 1 d horizon on
a 5-minute grid adjacent pairs share 287 of their 288 samples, so the filter
was handed the same outcome 288 times and RLS with forgetting read each one as
fresh evidence:

   horizon  steps  overlap  independent events in a 400-score window
       15m      3   66.7%    133.3
        1h     12   91.7%     33.3
        3h     36   97.2%     11.1
        6h     72   98.6%      5.6
       12h    144   99.3%      2.8
        1d    288   99.7%      1.4

The day-ahead head was therefore fitted on roughly two independent outcomes by
a filter carrying 667 updates of memory, and its interval was a 90th percentile
of a sample of size one.

This is not a compute shortcut that trades accuracy for speed. Measured
walk-forward on four days of real station data and averaged over five train
splits, striding improves every horizon past fifteen minutes:

   15m  +0.6%   1h -12.2%   3h -31.7%   6h -33.3%   12h -39.5%   1d -14.4%

with coverage unchanged at 87 to 92%, and the fit 11.6x faster. The redundancy
was not merely wasted work, it was collapsing P onto the one direction the
repeated sample excited.

The stride phase rotates each refit and is persisted, so a long-lived station
eventually trains on every offset rather than seeing one sample in 288 forever,
and a restart does not pin it to phase 0. A floor relaxes the stride when a
long horizon on a short record would otherwise yield one or two pairs; 12 was
chosen by sweeping it across five splits rather than picked.

Single-split runs showed 10 to 17% regressions at the 1 d horizon that moved
with the parameter. Averaging over five splits removed them, which is the
expected result for a head fitted and scored on under two independent
outcomes. That horizon cannot be evaluated on a four-day record and was not
tuned against.

Incidentally, this also retires the parallel-retrain idea: the Pi's 42 s
retrain becomes a few seconds, and multiprocessing inside a 280 MB cap buys
nothing for a job that short.
2026-08-19 18:50:07 +01:00
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