{
  "approach": "One delta on CH: replace the first-print absolute-return EMA by elapsed-normalized variance v=D*v+(1-D)*ret^2/max(1,timestamp-lastTs), with existing capped ret and WAD floors, and sigmaHat=floor(sqrt(v*WAD)). Initialize variance at (0.00095)^2. Slot 11 is the only additional slot; slots 0..11 used. No new loops: sqrt uses magnitude comparisons and seven unrolled Newton steps; CH's pre-existing bounded elapsed-decay loop remains. Keep CH's gate on the new sigmaHat, with its existing before-update ordering. Grid winner D69C20 selected solely by highest paired tuning mean on 10000..10499; n=500 each as item-specific brief permits. Frozen before any 600000..601999 simulation. Evaluate candidate and CH separately against the same 30-bps normalizer, never against each other, on identical per-seed configs. numpy.default_rng(seed) draws size U[19,21], rate U[0.6,1], sigma U[0.000882,0.001008], in that order; remaining settings match MatchRunner. Rust price seed=seed, retail seed=seed+1. run_batch chunks of 25; no simulator modifications. SE is sample sd/sqrt(n); worst means lowest candidate-minus-CH differences. Score uses seeds 0..999. Never used 900000..909999. seconds_per_simulation is total batch wall time / 10000 scored simulations, excluding setup, compilation, and scratch checks. Reference best remains CH 6dd68f77a70900319460215374143dbd5d924198450a46d9f5f91f6b1e3d35c3 with requester-provided seed-0..999 score 525.525882178 (not independently remeasured). Delivered code is the best requested variance candidate, even if losing; it is not an unqualified replacement for CH.",
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  "next": "Do not promote this variance delta: fresh paired difference is -0.286588741 with SE 0.017738248, n=2000. Retain CH. No promotions in this item. A later separate experiment could account for pHat filtering lag and retail measurement noise before interpreting squared implied-price deviations as per-step fair-price variance; this explanation is a hypothesis, not established by this grid.",
  "code": "// SPDX-License-Identifier: MIT\npragma solidity ^0.8.24;\n\nimport {AMMStrategyBase} from \"./AMMStrategyBase.sol\";\nimport {TradeInfo} from \"./IAMMStrategy.sol\";\n\ncontract Strategy is AMMStrategyBase {\n    uint256 constant ELAPSED_CAP = 8;\n    uint256 constant SIGNAL_THRESHOLD = WAD / 650;\n    uint256 constant DIR_DECAY = 750000000000000000;\n    uint256 constant ACT_DECAY = 530000000000000000;\n    uint256 constant SIZE_DECAY = 530000000000000000;\n    uint256 constant TOX_DECAY = 910000000000000000;\n    uint256 constant SIGMA_DECAY = 690000000000000000;\n    uint256 constant LAMBDA_DECAY = 990000000000000000;\n    uint256 constant SIZE_BLEND_DECAY = 828000000000000000;\n    uint256 constant TOX_BLEND_DECAY = 51000000000000000;\n    uint256 constant ACT_BLEND_DECAY = 985000000000000000;\n    uint256 constant PHAT_ALPHA = 270000000000000000;\n    uint256 constant PHAT_ALPHA_RETAIL = 60000000000000000;\n    uint256 constant DIR_IMPACT_MULT = 4;\n    uint256 constant GATE_SIGMA_MULT = 7200000000000000000;\n    uint256 constant MIN_GATE = 30000000000000000;\n    uint256 constant TRADE_TOX_BOOST = 3500 * BPS;\n    uint256 constant STALE_ATTRACT_FRAC = 1050000000000000000;\n    uint256 constant RET_CAP = WAD / 35;\n    uint256 constant TOX_CAP = WAD / 5;\n    uint256 constant TRADE_RATIO_CAP = WAD / 5;\n    uint256 constant LAMBDA_CAP = 1820000000000000000;\n    uint256 constant STEP_COUNT_CAP = 64;\n    uint256 constant BASE_FEE = 4 * BPS;\n    uint256 constant SIGMA_COEF = 200000000000000000;\n    uint256 constant LAMBDA_COEF = 12 * BPS;\n    uint256 constant FLOW_SIZE_COEF = 4842 * BPS;\n    uint256 constant TOX_COEF = 300 * BPS;\n    uint256 constant TOX_QUAD_COEF = 15000 * BPS;\n    uint256 constant ACT_COEF = 91843 * BPS;\n    uint256 constant DIR_COEF = 20 * BPS;\n    uint256 constant DIR_TOX_COEF = 100 * BPS;\n    uint256 constant STALE_DIR_COEF = 6850 * BPS;\n    uint256 constant SIGMA_TOX_COEF = 500 * BPS;\n    uint256 constant TAIL_KNEE = 600 * BPS;\n    uint256 constant TAIL_SLOPE_PROTECT = 930000000000000000;\n    uint256 constant TAIL_SLOPE_ATTRACT = 850000000000000000;\n\n    function afterInitialize(uint256 initialX, uint256 initialY) external override returns (uint256, uint256) {\n        slots[0] = BASE_FEE; slots[1] = BASE_FEE; slots[2] = 0; slots[3] = WAD; slots[4] = 0;\n        slots[5] = initialX > 0 ? wdiv(initialY, initialX) : 100 * WAD;\n        slots[6] = 950000000000000; slots[7] = 800000000000000000; slots[8] = 2000000000000000;\n        slots[9] = 0; slots[10] = 0; slots[11] = 902500000000;\n        return (BASE_FEE, BASE_FEE);\n    }\n\n    function afterSwap(TradeInfo calldata trade) external override returns (uint256, uint256) {\n        uint256 prevBidFee = slots[0]; uint256 prevAskFee = slots[1]; uint256 lastTs = slots[2];\n        uint256 dirState = slots[3]; uint256 actEma = slots[4]; uint256 pHat = slots[5];\n        uint256 sigmaHat = slots[6]; uint256 lambdaHat = slots[7]; uint256 sizeHat = slots[8];\n        uint256 toxEma = slots[9]; uint256 stepTradeCount = slots[10];\n\n        bool isNewStep = trade.timestamp > lastTs;\n        if (isNewStep) {\n            uint256 elapsedRaw = trade.timestamp - lastTs;\n            uint256 elapsed = elapsedRaw > ELAPSED_CAP ? ELAPSED_CAP : elapsedRaw;\n            dirState = _decayCentered(dirState, DIR_DECAY, elapsed);\n            actEma = wmul(actEma, _powWad(ACT_DECAY, elapsed));\n            sizeHat = wmul(sizeHat, _powWad(SIZE_DECAY, elapsed));\n            toxEma = wmul(toxEma, _powWad(TOX_DECAY, elapsed));\n            if (stepTradeCount > 0 && elapsedRaw > 0) {\n                uint256 lambdaInst = (stepTradeCount * WAD) / elapsedRaw;\n                if (lambdaInst > LAMBDA_CAP) lambdaInst = LAMBDA_CAP;\n                lambdaHat = wmul(lambdaHat, LAMBDA_DECAY) + wmul(lambdaInst, WAD - LAMBDA_DECAY);\n            }\n            stepTradeCount = 0;\n        }\n\n        bool firstInStep = stepTradeCount == 0;\n        uint256 spot = trade.reserveX > 0 ? wdiv(trade.reserveY, trade.reserveX) : pHat;\n        if (pHat == 0) pHat = spot;\n\n        uint256 feeUsed = trade.isBuy ? prevBidFee : prevAskFee;\n        uint256 gamma = feeUsed < WAD ? WAD - feeUsed : 0;\n        uint256 pImplied;\n        if (gamma == 0) { pImplied = spot; }\n        else { pImplied = trade.isBuy ? wmul(spot, gamma) : wdiv(spot, gamma); }\n\n        {\n            uint256 ret = pHat > 0 ? wdiv(absDiff(pImplied, pHat), pHat) : 0;\n            uint256 alpha = firstInStep ? PHAT_ALPHA : PHAT_ALPHA_RETAIL;\n            uint256 adaptiveGate = wmul(sigmaHat, GATE_SIGMA_MULT);\n            if (adaptiveGate < MIN_GATE) adaptiveGate = MIN_GATE;\n            if (ret <= adaptiveGate) { pHat = wmul(pHat, WAD - alpha) + wmul(pImplied, alpha); }\n            if (firstInStep) {\n                if (ret > RET_CAP) ret = RET_CAP;\n                uint256 elapsedRaw = trade.timestamp > lastTs ? trade.timestamp - lastTs : 1;\n                uint256 varianceHat = wmul(slots[11], SIGMA_DECAY)\n                    + wmul(wmul(ret, ret) / elapsedRaw, WAD - SIGMA_DECAY);\n                slots[11] = varianceHat;\n                sigmaHat = _isqrt(varianceHat * WAD);\n            }\n        }\n\n        uint256 tradeRatio = trade.reserveY > 0 ? wdiv(trade.amountY, trade.reserveY) : 0;\n        if (tradeRatio > TRADE_RATIO_CAP) tradeRatio = TRADE_RATIO_CAP;\n\n        if (tradeRatio > SIGNAL_THRESHOLD) {\n            uint256 push = tradeRatio * DIR_IMPACT_MULT;\n            if (push > WAD / 4) push = WAD / 4;\n            if (trade.isBuy) {\n                dirState = dirState + push;\n                if (dirState > 2 * WAD) dirState = 2 * WAD;\n            } else {\n                dirState = dirState > push ? dirState - push : 0;\n            }\n            actEma = wmul(actEma, ACT_BLEND_DECAY) + wmul(tradeRatio, WAD - ACT_BLEND_DECAY);\n            sizeHat = wmul(sizeHat, SIZE_BLEND_DECAY) + wmul(tradeRatio, WAD - SIZE_BLEND_DECAY);\n            if (sizeHat > WAD) sizeHat = WAD;\n        }\n\n        uint256 tox = pHat > 0 ? wdiv(absDiff(spot, pHat), pHat) : 0;\n        if (tox > TOX_CAP) tox = TOX_CAP;\n        toxEma = wmul(toxEma, TOX_BLEND_DECAY) + wmul(tox, WAD - TOX_BLEND_DECAY);\n        uint256 toxSignal = toxEma;\n\n        stepTradeCount = stepTradeCount + 1;\n        if (stepTradeCount > STEP_COUNT_CAP) stepTradeCount = STEP_COUNT_CAP;\n\n        uint256 flowSize = wmul(lambdaHat, sizeHat);\n        uint256 fBase = BASE_FEE + wmul(SIGMA_COEF, sigmaHat) + wmul(LAMBDA_COEF, lambdaHat) + wmul(FLOW_SIZE_COEF, flowSize);\n        uint256 fMid = fBase + wmul(TOX_COEF, toxSignal) + wmul(TOX_QUAD_COEF, wmul(toxSignal, toxSignal)) + wmul(ACT_COEF, actEma);\n        fMid = fMid + wmul(SIGMA_TOX_COEF, wmul(sigmaHat, toxSignal));\n\n        uint256 dirDev; bool sellPressure;\n        if (dirState >= WAD) { dirDev = dirState - WAD; sellPressure = true; }\n        else { dirDev = WAD - dirState; sellPressure = false; }\n\n        uint256 skew = wmul(DIR_COEF, dirDev) + wmul(DIR_TOX_COEF, wmul(dirDev, toxSignal));\n        uint256 bidFee; uint256 askFee;\n        if (sellPressure) {\n            bidFee = fMid + skew;\n            askFee = fMid > skew ? fMid - skew : 0;\n        } else {\n            askFee = fMid + skew;\n            bidFee = fMid > skew ? fMid - skew : 0;\n        }\n\n        {\n            uint256 staleShift = wmul(STALE_DIR_COEF, toxSignal);\n            uint256 attractShift = wmul(staleShift, STALE_ATTRACT_FRAC);\n            if (spot >= pHat) {\n                bidFee = bidFee + staleShift;\n                askFee = askFee > attractShift ? askFee - attractShift : 0;\n            } else {\n                askFee = askFee + staleShift;\n                bidFee = bidFee > attractShift ? bidFee - attractShift : 0;\n            }\n        }\n\n        {\n            bool tradeAligned = (trade.isBuy && spot >= pHat) || (!trade.isBuy && spot < pHat);\n            if (tradeAligned) {\n                uint256 tradeBoost = wmul(TRADE_TOX_BOOST, tradeRatio);\n                if (trade.isBuy) { bidFee = bidFee + tradeBoost; }\n                else { askFee = askFee + tradeBoost; }\n            }\n        }\n\n        if (sellPressure) {\n            bidFee = clampFee(_compressTailWithSlope(bidFee, TAIL_SLOPE_PROTECT));\n            askFee = clampFee(_compressTailWithSlope(askFee, TAIL_SLOPE_ATTRACT));\n        } else {\n            askFee = clampFee(_compressTailWithSlope(askFee, TAIL_SLOPE_PROTECT));\n            bidFee = clampFee(_compressTailWithSlope(bidFee, TAIL_SLOPE_ATTRACT));\n        }\n\n        slots[0] = bidFee; slots[1] = askFee; slots[2] = trade.timestamp;\n        slots[3] = dirState; slots[4] = actEma; slots[5] = pHat;\n        slots[6] = sigmaHat; slots[7] = lambdaHat; slots[8] = sizeHat;\n        slots[9] = toxEma; slots[10] = stepTradeCount;\n\n        return (bidFee, askFee);\n    }\n\n    function _isqrt(uint256 x) internal pure returns (uint256 z) {\n        if (x == 0) return 0;\n        uint256 y = x; z = 1;\n        if (y >> 128 > 0) { y >>= 128; z <<= 64; }\n        if (y >> 64 > 0) { y >>= 64; z <<= 32; }\n        if (y >> 32 > 0) { y >>= 32; z <<= 16; }\n        if (y >> 16 > 0) { y >>= 16; z <<= 8; }\n        if (y >> 8 > 0) { y >>= 8; z <<= 4; }\n        if (y >> 4 > 0) { y >>= 4; z <<= 2; }\n        if (y >> 2 > 0) { z <<= 1; }\n        unchecked {\n            z = (z + x / z) >> 1;\n            z = (z + x / z) >> 1;\n            z = (z + x / z) >> 1;\n            z = (z + x / z) >> 1;\n            z = (z + x / z) >> 1;\n            z = (z + x / z) >> 1;\n            z = (z + x / z) >> 1;\n            uint256 other = x / z;\n            if (other < z) z = other;\n        }\n    }\n\n    function _compressTailWithSlope(uint256 fee, uint256 slope) internal pure returns (uint256) {\n        if (fee <= TAIL_KNEE) return fee;\n        return TAIL_KNEE + wmul(fee - TAIL_KNEE, slope);\n    }\n\n    function _powWad(uint256 factor, uint256 exp) internal pure returns (uint256 result) {\n        result = WAD;\n        while (exp > 0) {\n            if (exp & 1 == 1) result = wmul(result, factor);\n            factor = wmul(factor, factor);\n            exp >>= 1;\n        }\n    }\n\n    function _decayCentered(uint256 centered, uint256 decayFactor, uint256 elapsed) internal pure returns (uint256) {\n        uint256 mul = _powWad(decayFactor, elapsed);\n        if (centered >= WAD) { return WAD + wmul(centered - WAD, mul); }\n        uint256 below = wmul(WAD - centered, mul);\n        return below < WAD ? WAD - below : 0;\n    }\n\n    function getName() external pure override returns (string memory) { return \"no_cubic\"; }\n}\n",
  "code_sha256": "3d8dfb6aa8607d3ca58dfeaa70772fcab75fd9d33d78fbd40e72151e64c40192",
  "delta": "Set SIGMA_DECAY=690000000000000000 and SIGMA_COEF=200000000000000000. Append slots[11] = 902500000000 to afterInitialize (WAD variance of 0.00095). Replace only the firstInStep sigma EMA line with: elapsedRaw = trade.timestamp > lastTs ? trade.timestamp-lastTs : 1; varianceHat = wmul(slots[11],SIGMA_DECAY) + wmul(wmul(ret,ret)/elapsedRaw,WAD-SIGMA_DECAY); slots[11]=varianceHat; sigmaHat=_isqrt(varianceHat*WAD). Insert _isqrt before _compressTailWithSlope: return 0 for x=0; seed z=1,y=x; for shifts 128,64,32,16,8,4 conditionally right-shift y and left-shift z by half that shift; if y>>2>0 left-shift z by 1; perform seven explicitly unrolled z=(z+x/z)>>1 steps unchecked; return min(z,x/z). Existing gate uses prior sigmaHat; slot 6 stores updated sigmaHat. All other source text unchanged.",
  "score": {
    "seed_start": 0,
    "n": 1000,
    "mean_edge": 525.2470928336927,
    "se": 2.790527584325092
  },
  "paired": {
    "reference": "CH 6dd68f77",
    "seed_start": 600000,
    "n": 2000,
    "mean_diff": -0.2865887410740618,
    "se": 0.01773824750410544,
    "worst": [
      {
        "seed": 600845,
        "candidate_edge": 371.42941081032615,
        "reference_edge": 387.67289987703776,
        "diff": -16.243489066711618
      },
      {
        "seed": 601728,
        "candidate_edge": 612.6061662878251,
        "reference_edge": 624.3542123549739,
        "diff": -11.748046067148834
      },
      {
        "seed": 601698,
        "candidate_edge": 499.6737389505853,
        "reference_edge": 506.5382363532637,
        "diff": -6.86449740267841
      },
      {
        "seed": 600930,
        "candidate_edge": 509.0555472337906,
        "reference_edge": 513.2886125731824,
        "diff": -4.233065339391771
      },
      {
        "seed": 600619,
        "candidate_edge": 489.245917266965,
        "reference_edge": 493.4679288405589,
        "diff": -4.222011573593875
      }
    ]
  },
  "seconds_per_simulation": 0.2996049558671424,
  "validate_ok": true,
  "blocked": null,
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/ChengHua926/amm-challenge/d34a5199c59a4c44d5336a25f1436b4ae1f21104/contracts/src/Strategy.sol",
      "used_for": "Verified CH source and baseline delta."
    },
    {
      "url": "https://raw.githubusercontent.com/benedictbrady/amm-challenge/6b6921f8d463314aa7c96234e1be25a25245f704/amm_competition/competition/match.py",
      "used_for": "Canonical paired configuration construction and seed-indexed parameter draw order."
    },
    {
      "url": "https://raw.githubusercontent.com/benedictbrady/amm-challenge/6b6921f8d463314aa7c96234e1be25a25245f704/amm_competition/competition/config.py",
      "used_for": "Canonical simulation ranges and fixed parameters."
    },
    {
      "url": "https://raw.githubusercontent.com/benedictbrady/amm-challenge/6b6921f8d463314aa7c96234e1be25a25245f704/amm_sim_rs/src/simulation/engine.rs",
      "used_for": "Rust price and retail seed handling."
    },
    {
      "url": "https://raw.githubusercontent.com/benedictbrady/amm-challenge/6b6921f8d463314aa7c96234e1be25a25245f704/amm_competition/evm/compiler.py",
      "used_for": "Compiler version, optimizer and viaIR pipeline."
    },
    {
      "url": "https://raw.githubusercontent.com/dipankar/amm-challenge/main/ANALYSIS.md",
      "used_for": "Public background write-up: advocates implied-price state estimation and adaptive volatility gating. Its claimed scores were not used as measurements in this item."
    },
    {
      "url": "https://raw.githubusercontent.com/benedictbrady/amm-challenge/6b6921f8d463314aa7c96234e1be25a25245f704/amm_sim_rs/src/evm/strategy.rs",
      "used_for": "Rust engine initialization and trade gas limits are 250000."
    },
    {
      "kind": "local measurements (this item)",
      "used_for": "All tried, score, paired and timing numbers are local run_batch measurements. Starter, CH, and selected strategy pass amm-match validate; EVM helper harness checks 2007 integer-square-root vectors and 300 synthetic swaps at 250000 gas. Exact variance-storage checks also pass for timestamp zero, repeated timestamps, and uncapped elapsed gaps 2, 27, 50. No exact gas-use estimate is claimed. Paradigm puzzle page could not be retrieved through web tool; no live leaderboard verification claimed."
    }
  ]
}
