smith6jt-cop Capital Manager Proportional Limits
Experiment Overview
| Item | Details |
|---|---|
| Date | 2024-12-24 |
| Goal | Fix capital manager blocking trades with hard-coded dollar amounts |
| Environment | scripts/live_trader.py, alpaca_trading/risk/capital_manager.py |
| Status | Success |
Context
The capital manager was initialized with min_cash_buffer=1000.0 - a fixed dollar amount that:
- Blocked 20% of a $5,000 account - Leaving only $4,000 for trading
- Blocked 10% of a $10,000 account - Still significant
- Blocked only 1% of a $100,000 account - Negligible
The 30% safety buffer (percentage-based) already provides proportional protection. The extra $1,000 was redundant and harmful for smaller accounts.
Verified Workflow
Problem Pattern
# WRONG: Hard-coded dollar amount
capital_mgr = CapitalManager(
safety_buffer_pct=0.30,
trading_allocation_pct=0.70,
max_position_pct=0.20,
min_cash_buffer=1000.0 # <-- Blocks 20% of $5k account!
)
Solution: Use Percentage-Based Limits
# CORRECT: Let percentage-based safety buffer handle it
capital_mgr = CapitalManager(
safety_buffer_pct=0.30, # 30% safety buffer (proportional)
trading_allocation_pct=0.70, # 70% available for trading
max_position_pct=0.20, # 20% max per position
# min_cash_buffer defaults to 0.0 - safety buffer is proportional
)
Capital Manager Design
The CapitalManager class is correctly designed with percentage-based defaults:
class CapitalManager:
def __init__(
self,
safety_buffer_pct: float = 0.30, # 30% reserved
trading_allocation_pct: float = 0.70, # 70% for trading
max_position_pct: float = 0.20, # 20% max per position
min_cash_buffer: float = 0.0, # Additional cash buffer (default: none)
min_trade_value: float = 1.0 # Supports fractional shares
):
The min_cash_buffer parameter exists for edge cases but should rarely be used since the percentage-based safety buffer already scales with account size.
Impact Analysis
| Account Size | Old (with $1,000 buffer) | New (0% buffer) | Improvement |
|---|---|---|---|
| $5,000 | $4,000 available | $5,000 available | +25% |
| $10,000 | $9,000 available | $10,000 available | +11% |
| $50,000 | $49,000 available | $50,000 available | +2% |
| $100,000 | $99,000 available | $100,000 available | +1% |
Note: The 30% safety buffer still applies to all accounts, so actual trading capital is 70% of these values.
Failed Attempts (Critical)
| Attempt | Why it Failed | Lesson Learned |
|---|---|---|
| Hard-coded $1,000 min_cash_buffer | Disproportionately hurt small accounts | Use percentage-based limits only |
| Hard-coded $50 in strategies | Same problem at smaller scale | Remove absolute dollar amounts |
| Fixed confidence thresholds | Didn't adapt to volatility regimes | Consider adaptive thresholds |
| Hard-coded stop-loss percentages | Didn't account for asset volatility | Consider asset-specific thresholds |
Key Insights
Percentage-Based vs Dollar-Based
| Approach | Pros | Cons | When to Use |
|---|---|---|---|
| Percentage-based | Scales with account, fair to all sizes | May allow tiny trades on small accounts | Default - almost always |
| Dollar-based | Prevents dust trades | Unfair to small accounts, doesn't scale | Only for minimum trade value |
Other Hard-Coded Values to Watch
These were identified during investigation (not fixed yet):
# In live_trader.py - consider making configurable:
confidence = 0.6 # Default fallback confidence
rl_confidence < 0.4 # Minimum RL confidence threshold
confidence < 0.70 # Extreme volatility threshold
base_breakeven = 0.02 # 2% breakeven stop
base_trailing = 0.05 # 5% trailing stop
# In harmonized.py:
min_cash_buffer = 50.0 # Should also be removed
The 30% Safety Buffer
The existing safety buffer provides strong protection:
# How it works:
conservative_value = account_value - unrealized_profits + unrealized_losses
safety_buffer = conservative_value * 0.30 # 30% reserved
available_capital = conservative_value * 0.70 # 70% for trading
# For a $10,000 account:
# - Safety buffer: $3,000 (never touched)
# - Trading capital: $7,000
# - Max per position: $1,400 (20% of $7,000)
Files Modified
scripts/live_trader.py:
- Line 1751-1756: Removed min_cash_buffer=1000.0
- Added comment explaining proportional protection
References
alpaca_trading/risk/capital_manager.py: Lines 74-100 (class design)scripts/live_trader.py: Lines 1750-1757 (initialization)- CLAUDE.md: Risk Controls section