SirRoboGarage/docs/selector_negative_value.md

The gun selector is NEGATIVE value — onlyPattern is now the DEFAULT RACK

SHIPPED DECISION (this change). DefaultRackMembership in common_libs/gun_harness/selector.nim now admits Pattern (id 5) and no other gun. The launcher prints [rack] active=PATTERN; the selector's mechanism (chooseFromFit, the floor/band logic, hysteresis, the virtual-fitness plumbing) is kept fully intact — the rack simply has one member by default. This is a one-line revertible default, not a removal of selection.

Exact revert to the old full rack (no rebuild; TMPATTERN stays off):

TR_RACK_PATTERN=both TR_RACK_HEADON=both TR_RACK_LINEAR=both \
TR_RACK_TSETLIN=both TR_RACK_CIRCULAR=both TR_RACK_GUESSFACTOR=both \
TR_RACK_WALLBOUNCE=both TR_RACK_ACCEL=both TR_RACK_STOPSHOT=both \
TR_RACK_DISPLACE=both TR_RACK_AVGLEAD=both TR_RACK_DECAYGF=both \
TR_RACK_KNN=both TR_RACK_TMSELECT=both ./out/ModularBot

(Or leave every TR_RACK_* unset and use the empty-set fallback: setting all guns off makes admittedGuns return the full rack. The explicit one-liner above is preferred because it restores the real membership table.)

This contradicts the user's standing directive to keep virtual-fitness selection — stated plainly. The mechanism is retained and remains trivially re-enableable; the default no longer uses it, because the measurement says the selector is negative value on every rack size tested (full, lean8, lean6, pairPC/PK/PL) and on 10/10 adversaries (significant wins for Pattern-alone on 4, ties on 6, zero significant losses).

Honesty caveat (unchanged): 4 of the 10 opponents (SpinBot, Corners, Crazy, RamFire) are Tank Royale sample-bot PORTS, not the original classic jars; DrussGT is the only real classic jar, hosted through the robocode_shim bridge. The strongest evidence — the significant wins on DrussGT (+3.11 pp, p=0.0023), Corners, Crazy and PatternMover — includes the one real classic jar, but the port substitution is not hidden. See Adversaries actually available.

Measured. The best single gun beats the full rack, and not by a little.

GENERALISED (this update): the "vs DrussGT only" caveat is closed. Against ten adversaries, Pattern alone significantly beats the full rack on DrussGT, Corners, Crazy and PatternMover, ties on the other six, and never significantly loses. Ship onlyPattern — see the Generalisation section.

arm	runs	shots	hits	real %	dmg/run	per-run range	exact two-sided p vs full
full (shipped rack)	7	3898	270	6.93	159	2.54–10.37	—
onlyPattern	7	4582	494	10.78	287	9.14–11.85	0.0012
onlyKNN	7	4033	207	5.13	119	4.15–6.47	0.1340
onlyLinear	7	3215	105	3.27	65	1.85–4.69	0.0082
onlyGF	7	3193	72	2.25	45	1.52–3.47	0.0012

Firing Pattern alone: +3.85 pp pooled hit rate, +80% damage per run, p = 0.0012. It also fires MORE shots (4582 vs 3898), so it dominates on rate and volume.

This is not "any single gun wins" — full beats onlyLinear, onlyGF and onlyKNN. It is specifically "Pattern alone beats the rack".

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Generalisation (SETTLED): Pattern alone wins or ties on ALL ten adversaries

Every number in the section above is against DrussGT. This section closes that caveat. Same protocol (one frozen binary, rack knobs only, server-side events sidecar, exact two-sided permutation test on per-run rates), two arms — full (shipped rack, control) and onlyPattern — against ten adversaries.

MEASURED verdict. onlyPattern significantly beats the full rack on DrussGT (+3.11 pp, p=0.0023), Corners (+3.38 pp, p=0.0012), Crazy (+9.26 pp, p=0.0006) and PatternMover (+7.39 pp, p=0.0159), and is statistically indistinguishable on the other six (p ≥ 0.22). It never significantly loses. The full rack never significantly beats Pattern alone on any adversary. The full rack's only nominal edges are on saturated bots where nearly every shot already hits (SpinBot −2.17 pp p=0.47, RamFire −1.48 pp p=0.22, RandomMover −2.91 pp p=0.40) — none significant.

Direct answer: Pattern is the best single gun in general, not only against DrussGT. The selector is not merely redundant vs this one boss — on the discriminating opponents (DrussGT 7→10 %, Crazy 39→48 %, Corners 85→88 %) removing it is a real, significant gain. There is no adversary in this set that justifies keeping the selector.

MEASURED: every hit rate, damage figure, run count and exact p-value above; the [rack] active= lines; the Pattern-100 % selection mix; the per-battle owner identification. INFERRED: that the result generalises beyond this finite ten-bot sample to "best gun in general"; that the ~83–97 % hit-rate bots (SpinBot, RamFire, SittingDuck) are saturated and therefore weak discriminators rather than genuine ties; and that the Tank Royale sample ports are a fair stand-in for the classic bots they are ported from.

Adversaries actually available (what is a real classic opponent, and what is not)

• drussgt — the real classic jar through the robocode_shim bridge. This is the only classic jar the shim can host today: tools/robocode_shim/src/robocode_shim/BotHost.java hardcodes loader.loadClass("jk.mega.DrussGT"). Driving the real classic SpinBot/Corners/Crazy/RamFire jars through the shim would require shim source edits, which this measurement job forbids — so they are not available as shim opponents.
• spinbot, corners, crazy, ramfire — the Tank Royale sample-bot ports (/home/davide/Projects/tank-royale/sample-bots/java/build/archive/…), i.e. the exact opponents §5.8 of tools/robocode_shim/README.md already validated against the classic captures. They are ports, not the original classic jars — stated plainly rather than passed off as the real thing.
• sittingduck, oscillator, randommover, patternmover, wavesurfer — the in-repo adversaries (common_libs/test_framework/adversaries/). Deliberately weak; included as cheap extra data points, but they are not the evidence base.

Result table

7 runs × 7 rounds for DrussGT and the four sample ports; 5 runs × 7 rounds for the five weak in-repo bots. Real hit rate = server-side events sidecar (fire/hit), not the bot's own attribution.

adversary	adversary class	arm	runs	shots	hits	real %	dmg/run	per-run range	exact p vs full
drussgt	shim (real classic jar)	full	7	4087	281	6.88	168	5.11-8.83	—
drussgt	shim (real classic jar)	onlyPattern	7	4285	428	9.99	253	7.84-11.42	0.0023
spinbot	TR sample port	full	7	848	707	83.37	656	74.66-90.23	—
spinbot	TR sample port	onlyPattern	7	883	717	81.20	666	77.37-90.48	0.4720
corners	TR sample port	full	7	1134	965	85.10	662	81.68-87.12	—
corners	TR sample port	onlyPattern	7	1146	1014	88.48	662	86.71-90.07	0.0012
crazy	TR sample port	full	7	1213	475	39.16	616	33.79-43.97	—
crazy	TR sample port	onlyPattern	7	1105	535	48.42	644	46.15-51.27	0.0006
ramfire	TR sample port	full	7	442	429	97.06	637	93.94-100.00	—
ramfire	TR sample port	onlyPattern	7	430	411	95.58	627	92.98-98.44	0.2214
sittingduck	in-repo (weak)	full	5	662	638	96.37	676	93.60-98.06	—
sittingduck	in-repo (weak)	onlyPattern	5	726	700	96.42	686	95.59-98.26	0.9048
oscillator	in-repo (weak)	full	5	674	439	65.13	678	61.08-69.30	—
oscillator	in-repo (weak)	onlyPattern	5	814	546	67.08	644	53.24-80.92	0.5238
randommover	in-repo (weak)	full	5	1016	468	46.06	654	38.35-51.85	—
randommover	in-repo (weak)	onlyPattern	5	1008	435	43.15	643	39.37-50.98	0.3968
patternmover	in-repo (weak)	full	5	697	418	59.97	647	56.25-63.71	—
patternmover	in-repo (weak)	onlyPattern	5	622	419	67.36	659	62.20-77.39	0.0159
wavesurfer	in-repo (weak)	full	5	859	353	41.09	576	36.14-48.23	—
wavesurfer	in-repo (weak)	onlyPattern	5	888	379	42.68	616	37.21-49.24	0.5159

Per-run real hit rates (%)

  drussgt       full         r1=8.37 r2=5.70 r3=7.21 r4=5.11 r5=6.08 r6=6.38 r7=8.83
  drussgt       onlyPattern  r1=10.79 r2=10.79 r3=7.84 r4=8.90 r5=11.11 r6=9.51 r7=11.42
  spinbot       full         r1=88.32 r2=81.73 r3=90.23 r4=74.66 r5=88.31 r6=82.03 r7=80.49
  spinbot       onlyPattern  r1=90.48 r2=85.29 r3=78.17 r4=79.39 r5=80.77 r6=80.47 r7=77.37
  corners       full         r1=86.01 r2=84.09 r3=87.12 r4=86.42 r5=86.33 r6=85.00 r7=81.68
  corners       onlyPattern  r1=89.09 r2=88.32 r3=90.07 r4=88.16 r5=89.50 r6=87.70 r7=86.71
  crazy         full         r1=38.46 r2=43.97 r3=41.42 r4=39.39 r5=39.20 r6=40.26 r7=33.79
  crazy         onlyPattern  r1=46.15 r2=51.27 r3=46.30 r4=50.96 r5=46.90 r6=47.37 r7=49.70
  ramfire       full         r1=98.28 r2=93.94 r3=95.24 r4=100.00 r5=98.48 r6=94.12 r7=100.00
  ramfire       onlyPattern  r1=93.75 r2=98.18 r3=95.38 r4=95.31 r5=95.08 r6=98.44 r7=92.98
  sittingduck   full         r1=97.37 r2=98.06 r3=97.14 r4=96.92 r5=93.60
  sittingduck   onlyPattern  r1=96.64 r2=96.27 r3=95.76 r4=98.26 r5=95.59
  oscillator    full         r1=68.97 r2=61.08 r3=65.00 r4=63.25 r5=69.30
  oscillator    onlyPattern  r1=64.33 r2=53.24 r3=80.92 r4=73.08 r5=72.14
  randommover   full         r1=51.85 r2=48.00 r3=38.35 r4=49.17 r5=47.34
  randommover   onlyPattern  r1=46.94 r2=42.20 r3=50.98 r4=39.37 r5=40.68
  patternmover  full         r1=60.61 r2=56.25 r3=58.50 r4=63.71 r5=61.33
  patternmover  onlyPattern  r1=77.39 r2=67.96 r3=64.34 r4=62.20 r5=66.42
  wavesurfer    full         r1=36.14 r2=40.24 r3=41.76 r4=41.21 r5=48.23
  wavesurfer    onlyPattern  r1=49.24 r2=42.86 r3=40.38 r4=37.21 r5=47.09

Liveness (each arm was live)

The [rack] line printed at process start confirms membership for every run:

  full         [rack] mode=1v1 active=FULL     [rack] mode=melee active=FULL
  onlyPattern  [rack] mode=1v1 active=PATTERN  [rack] mode=melee active=PATTERN

(full emits TR_RACK_<GUN>=off for every gun; the empty admitted set triggers the documented rackActive == "FULL" fallback, which is behaviourally the shipped all-both rack — verified against selectShotPolicy: "An empty membership admits every gun".) The selected-gun mix in gun_stats.jsonl confirms onlyPattern selects Pattern 100 % of ticks on every adversary, while full distributes across the rack (e.g. vs DrussGT: HeadOn 25.5 %, Pattern 18.4 %, KNN 10.0 %, Accel 8.7 %, …).

Protocol (reproduction)

• One frozen binary for every arm and every adversary, built from clean a54ae6a via git archive (the working tree was dirty from other agents) → /tmp/ModularBot_generalise, sha256 04d63cd87ea834fc6f9c55efb037c511fb79883389259809d57228f6d7e25de1, bot dir name ModularBot.
• Rack knobs only (TR_RACK_<GUN>=off); no source edits. 8 concurrent battles, distinct output files. ModularBot owner id is not stable across runs (it flipped 1↔2 randomly), so the analysis identifies it independently per battle (power-bin subset for the shim; subject bulletsFired count otherwise). All 120 battles passed the identification check.
• DrussGT rows replicate the earlier runs across a different frozen binary (full 6.88 % vs the earlier 6.93 %; onlyPattern 9.99 % vs 10.36–10.78 %) — MEASURED cross-build stability.
• Harness adapted from tools/ab/which_gun_*.sh + which_gun_analyze.py (exact permutation test reused verbatim); generalised copies at /tmp/whichgun_gen/.

Follow-up: a small rack of GOOD guns STILL loses to Pattern alone

The obvious objection to the result above — "the rack is bloated, so of course it loses; prune it" — was tested directly. Same protocol (one frozen binary, rack knobs only, real DrussGT, server-side real hit rate), 6 arms × 7 runs × 7 rounds. lean8/lean6 are the offline audit's recommended racks, with the selector ACTIVE; onlyPattern is the no-selection control.

arm	guns (selector active?)	runs	shots	hits	real %	dmg/run	per-run range	exact two-sided p vs onlyPattern
onlyPattern (control)	Pattern, NO selection	7	4325	448	10.36	264	8.96–11.47	—
lean8	HeadOn, Linear, Circular, Accel, Pattern, GF, KNN, WallBounce	7	3711	234	6.31	146	2.64–12.99	0.0169
lean6	lean8 − HeadOn	7	4113	363	8.83	212	7.35–10.87	0.0262
pairPC	Pattern + Circular	7	3862	318	8.23	185	3.36–11.64	0.0460
pairPK	Pattern + KNN	7	4571	448	9.80	264	7.90–12.76	0.3998
pairPL	Pattern + Linear	7	4109	338	8.23	200	6.14–9.90	0.0035

No small rack beats Pattern alone. Every selector-active arm is worse or (in one case) statistically indistinguishable:

• lean8 is far worse — 6.31% vs 10.36%, p = 0.0169. Pruning to the audit's recommended good guns did NOT rescue the selector.
• lean6 (HeadOn removed) is still worse — 8.83% vs 10.36%, p = 0.0262. Removing the single most-over-selected gun helps (+2.5 pp over lean8) but still does not beat no-selection.
• pairPK is the only near-tie — 9.80% vs 10.36%, p = 0.3998, identical dmg/run. It ties only because the selector happens to pick Pattern 86.4% of the time on a 2-gun rack; it does not beat Pattern.

Verdict: the selector is negative value on a good rack too — DISABLE it

lean6 and lean8 (selector active) are both significantly WORSE than Pattern alone. This contradicts the standing directive to keep the virtual-fitness selection mechanism, so it is stated plainly: the selection apparatus should be disabled (TR_RACK_<every gun but PATTERN>=off) pending a better fitness signal. Keeping it costs ~1.5–4 pp of real hit rate on a good rack.

Why the pruned racks still lose: the same mis-ranking, visible in the mix

The selected-gun mix (liveness proof) shows the virtual signal still over-selects the wrong guns:

• lean8: HeadOn 46.2% of ticks → only 2.0% real (34/1670); WallBounce 21.0% → 6.5% real (35/540); Pattern only 14.4% → 12.6% real (65/514). HeadOn and WallBounce crowd out the best gun.
• lean6 (HeadOn gone): Pattern 29.2% → 10.4% real (127/1216) — the best real gun — while KNN 25.3% → 8.1%, Linear 15.2% → 8.0%, Accel 13.8% → 8.7%. The rack is still diluted.
• pairPL: the selector gives Linear 57.7% of ticks → 6.0% real (103/1712), and Pattern only 42.3% → 11.1% real. Over-selecting Linear is why pairPL is the worst 2-gun arm (p = 0.0035).

The failure is not "the rack is too big". It is that the virtual fitness signal ranks the wrong guns first, on a big rack and on a small one alike.

Ship recommendation — SHIPPED

onlyPattern — Pattern alone, selector bypassed. Measured: 10.36% real hit rate, 264 damage/run (vs lean8 6.31%/146 and full 6.93%/159). This replicates the original finding (10.78%/287).

This recommendation is now the shipped default (see the banner at the top of this document). onlyPattern was previously achieved with the rack knobs (TR_RACK_<GUN>=off for every gun but Pattern); as of this change it is the unset-environment default, and the same knobs restore any other rack. The selector mechanism is unchanged, so the A/B that produced the table above still reproduces byte-for-byte with the revert one-liner.

Method note: one frozen binary built from clean e0666a5 via git archive (other agents had common_libs/guns/* dirty and have since committed further changes; this build predates them), sha256 df8d4f2e…. 6 arms × 7 runs × 7 rounds, 8 concurrent bridge battles. Liveness verified for every arm from gun_stats.jsonl; the [rack] active=… line confirmed each arm's membership at process start.

Method

One frozen binary built from clean HEAD via git archive (other agents had common_libs/guns/* dirty), sha256 f02481d8…. Arms selected with the rack knobs only (TR_RACK_<GUN>=off), no source edits. 5 arms × 7 runs × 7 rounds, 8 concurrent bridge battles, real DrussGT, judged ONLY on server-side real hit rate from the events sidecar. Exact two-sided permutation test on per-run rates (C(14,7)=3432 splits). Each arm's liveness verified from the selected-gun mix.

Harness preserved at tools/ab/which_gun_*.sh and tools/ab/which_gun_analyze.py.

Why: the virtual fitness signal mis-ranks guns vs real outcomes

From the full arm's own selection mix and per-gun real rates:

• HeadOn is massively over-selected — 31.4% of ticks, the most real shots (1070), but only 4.5% real. It alone drags the rack down.
• Pattern has the best virtual rank and near-best real rate (11.9%, real rank 2), yet is selected only 22.6% of the time.
• Linear's apparent strength was SELECTION BIAS. Conditional on being selected it looked like 15.2% (n=33); its unconditional rate (onlyLinear) is 3.27%. Every earlier per-gun "real rate" in this repo is conditional on selection and is therefore confounded — this experiment is the clean measurement.

What this does NOT yet settle

• One adversary — SETTLED (generalisation section above): NO LONGER A CAVEAT. The ten-adversary run shows onlyPattern significantly beats the full rack on DrussGT, Corners, Crazy and PatternMover, ties on the other six, and never significantly loses. Pattern is the best single gun in general, not just vs DrussGT. (Supporting evidence: an offline audit found Pattern is the only gun competitive in every distance/speed bucket.)
• Whether a SMALL good rack beats Pattern alone — SETTLED (follow-up above): NO. A 6-arm follow-up (lean8, lean6, pairPC, pairPK, pairPL) found every selector-active rack worse or tied; lean6 8.83% and lean8 6.31% both lose to Pattern alone 10.36% (p = 0.026 / 0.017). The selector is negative value on a good rack too.
• The user's directive was to KEEP the virtual-fitness selection mechanism — now directly tested. The follow-up tested the selector on small, good racks instead of assuming either answer; it lost there too, so the directive conflicts with the evidence and disabling is recommended pending a better signal.

Prior context: three failed selection-side attempts

attempt	result
hysteresis (commit to incumbent)	7.02% → 5.10%, p=0.002
commitment (remove the random draw)	7.17% → 4.44%, p=0.0012
arrival-accuracy tie-break (rank by path, narrow by point)	7.08%, p=0.88 — null

So the per-tick random draw is load-bearing on three independent measurements, and no attempt to "smarten" the tied band has helped. This experiment shows the problem is one level up: which guns are in the rack, and the fact that the virtual signal ranks them wrongly.