feat(backtest): add SquareRootSlippage + VolumeSlippage

src/easy_tdx/backtest/slippage.py

@@ -4,6 +4,8 @@ from __future__ import annotations
 
 from abc import ABC, abstractmethod
 
+import numpy as np
+
 
 class SlippageModel(ABC):
     """滑点模型基类。
@@ -67,3 +69,61 @@ class PercentSlippage(SlippageModel):
         direction: str,
     ) -> float:
         return price * size * self._rate
+
+
+class SquareRootSlippage(SlippageModel):
+    """方根市场冲击模型（Almgren-Chriss 简化版）。
+
+    impact = σ × √(participation_rate) × price × size × impact_coeff
+
+    当 volume=0 或 volatility=0 时退化为 PercentSlippage(rate=0.001)。
+    """
+
+    def __init__(self, impact_coeff: float = 0.1) -> None:
+        self._impact_coeff = impact_coeff
+        self._fallback = PercentSlippage(rate=0.001)
+
+    def compute(
+        self,
+        price: float,
+        size: float,
+        volume: float,
+        volatility: float,
+        direction: str,
+    ) -> float:
+        if size <= 0:
+            return 0.0
+        if volume <= 0 or volatility <= 0:
+            return self._fallback.compute(price, size, volume, volatility, direction)
+        participation_rate = min(size / volume, 1.0)
+        impact = volatility * np.sqrt(participation_rate) * price * size * self._impact_coeff
+        return float(impact)
+
+
+class VolumeSlippage(SlippageModel):
+    """成交量比例滑点。
+
+    cost = (base_bps / 10000) × (size / volume) × price × size
+
+    当 volume=0 时退化为 PercentSlippage(rate=base_bps/10000)。
+    """
+
+    def __init__(self, base_bps: float = 10.0) -> None:
+        self._base_bps = base_bps
+        self._fallback = PercentSlippage(rate=base_bps / 10000.0)
+
+    def compute(
+        self,
+        price: float,
+        size: float,
+        volume: float,
+        volatility: float,
+        direction: str,
+    ) -> float:
+        if size <= 0:
+            return 0.0
+        if volume <= 0:
+            return self._fallback.compute(price, size, volume, volatility, direction)
+        rate = self._base_bps / 10000.0
+        participation = min(size / volume, 1.0)
+        return rate * participation * price * size

tests/unit/test_backtest_slippage.py

@@ -8,6 +8,8 @@ from easy_tdx.backtest.slippage import (
     FixedSlippage,
     PercentSlippage,
     SlippageModel,
+    SquareRootSlippage,
+    VolumeSlippage,
 )
 
 
@@ -85,3 +87,75 @@ class TestPercentSlippage:
         cost = model.compute(price=100.0, size=500, volume=20000, volatility=0.25, direction="BUY")
         # 100 × 500 × 0.002 = 100.0
         assert cost == pytest.approx(100.0)
+
+
+class TestSquareRootSlippage:
+    """方根市场冲击模型。"""
+
+    def test_zero_size(self) -> None:
+        """size=0 时无冲击。"""
+        model = SquareRootSlippage(impact_coeff=0.1)
+        cost = model.compute(price=10.0, size=0, volume=10000, volatility=0.3, direction="BUY")
+        assert cost == 0.0
+
+    def test_small_participation_rate(self) -> None:
+        """低参与率（小单），冲击成本低。"""
+        model = SquareRootSlippage(impact_coeff=0.1)
+        # size=100, volume=1000000, participation_rate=0.0001
+        cost = model.compute(
+            price=10.0, size=100, volume=1_000_000, volatility=0.3, direction="BUY"
+        )
+        # σ=0.3, √(0.0001)=0.01, impact = 0.3 × 0.01 × 10 × 100 × 0.1 = 0.3
+        assert cost == pytest.approx(0.3)
+
+    def test_high_participation_rate(self) -> None:
+        """高参与率（大单），冲击成本高。"""
+        model = SquareRootSlippage(impact_coeff=0.1)
+        cost = model.compute(
+            price=10.0, size=100_000, volume=200_000, volatility=0.3, direction="BUY"
+        )
+        small_cost = model.compute(
+            price=10.0, size=100, volume=1_000_000, volatility=0.3, direction="BUY"
+        )
+        assert cost > small_cost * 10
+
+    def test_zero_volume_fallback(self) -> None:
+        """volume=0 时退化为 PercentSlippage(rate=0.001)。"""
+        model = SquareRootSlippage(impact_coeff=0.1)
+        cost = model.compute(price=10.0, size=100, volume=0, volatility=0.3, direction="BUY")
+        assert cost == pytest.approx(1.0)
+
+    def test_zero_volatility_fallback(self) -> None:
+        """volatility=0 时退化为 PercentSlippage(rate=0.001)。"""
+        model = SquareRootSlippage(impact_coeff=0.1)
+        cost = model.compute(price=10.0, size=100, volume=10000, volatility=0.0, direction="BUY")
+        assert cost == pytest.approx(1.0)
+
+
+class TestVolumeSlippage:
+    """成交量比例滑点。"""
+
+    def test_zero_size(self) -> None:
+        model = VolumeSlippage(base_bps=10.0)
+        cost = model.compute(price=10.0, size=0, volume=10000, volatility=0.3, direction="BUY")
+        assert cost == 0.0
+
+    def test_basic(self) -> None:
+        model = VolumeSlippage(base_bps=10.0)
+        cost = model.compute(price=10.0, size=100, volume=10000, volatility=0.3, direction="BUY")
+        assert cost == pytest.approx(0.01)
+
+    def test_high_participation(self) -> None:
+        model = VolumeSlippage(base_bps=10.0)
+        cost_high = model.compute(
+            price=10.0, size=5000, volume=10000, volatility=0.3, direction="BUY"
+        )
+        cost_low = model.compute(
+            price=10.0, size=100, volume=10000, volatility=0.3, direction="BUY"
+        )
+        assert cost_high > cost_low
+
+    def test_zero_volume_fallback(self) -> None:
+        model = VolumeSlippage(base_bps=10.0)
+        cost = model.compute(price=10.0, size=100, volume=0, volatility=0.3, direction="BUY")
+        assert cost == pytest.approx(1.0)