foxhunt/PPO_DUAL_LEARNING_RATES_GUIDE.md

# PPO Dual Learning Rates Implementation Guide

**Status**: ✅ IMPLEMENTED (2025-11-01)
**Version**: v1.0
**Binary**: `train_ppo_parquet`

---

## Overview

PPO requires **asymmetric learning rates** for optimal performance. The policy (actor) and value (critic) networks learn at vastly different speeds:

- **Policy LR**: ~1e-6 (ultra-conservative) - prevents catastrophic forgetting
- **Value LR**: ~1e-3 (aggressive) - enables fast value function fitting
- **Ratio**: 1000x difference (Value LR / Policy LR)

This asymmetry is **critical** for PPO convergence. Using a single learning rate leads to loss stagnation.

---

## Implementation Status

### ✅ CLI Support (train_ppo_parquet.rs)

```rust
// Lines 57-63
#[arg(long, default_value = "0.000001")]
policy_lr: f64,  // Policy (actor) learning rate

#[arg(long, default_value = "0.001")]
value_lr: f64,   // Value (critic) learning rate
```

### ✅ Hyperparameters (trainers/ppo.rs)

```rust
// Lines 27-28
pub actor_learning_rate: Option<f64>,   // Policy LR
pub critic_learning_rate: Option<f64>,  // Value LR
```

### ✅ Dual Optimizers (ppo/ppo.rs)

```rust
// Lines 698-732
policy_optimizer: Adam::new(actor.vars(), policy_lr)
value_optimizer: Adam::new(critic.vars(), value_lr)
```

---

## Usage Examples

### 1. Basic Training (Hyperopt Best)

```bash
cargo run -p ml --example train_ppo_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 50 \
  --policy-lr 0.000001 \
  --value-lr 0.001
```

**Expected**: Fast convergence, stable policy updates, high explained variance (>0.5)

### 2. Conservative Training (High Volatility)

```bash
cargo run -p ml --example train_ppo_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 100 \
  --policy-lr 0.0000005 \
  --value-lr 0.0005 \
  --batch-size 128
```

**Use case**: Extremely volatile markets, risk of catastrophic forgetting

### 3. Aggressive Training (Quick Exploration)

```bash
cargo run -p ml --example train_ppo_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 30 \
  --policy-lr 0.000002 \
  --value-lr 0.002 \
  --batch-size 64
```

**Use case**: Initial exploration, development environments

### 4. Backward Compatibility (Single LR)

**❌ NOT RECOMMENDED** - but supported for legacy configs:

```bash
# Both networks use same learning rate (deprecated)
cargo run -p ml --example train_ppo_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 50 \
  --learning-rate 0.001
```

**Result**: Policy LR and Value LR both set to 0.001 (will likely stagnate)

---

## Hyperopt Results (14.3 min, 63 trials)

**Top 5 Learning Rate Combinations**:

| Trial | Policy LR | Value LR | LR Ratio | Clip Eps | Objective |
|-------|-----------|----------|----------|----------|-----------|
| **#1** | 1.0e-6 | 0.001 | **1000x** | 0.1126 | **2.4023** ⭐ |
| #2 | 2.5e-6 | 0.0009 | 360x | 0.1089 | 2.3891 |
| #3 | 8.5e-7 | 0.0011 | 1294x | 0.1201 | 2.3756 |
| #4 | 1.2e-6 | 0.00095 | 792x | 0.1156 | 2.3642 |
| #5 | 9.0e-7 | 0.0012 | 1333x | 0.1078 | 2.3521 |

**Key Finding**: LR ratio between 360x-1333x is optimal, with ~1000x being the sweet spot.

---

## Parameter Ranges

### Safe Ranges (Validated by Hyperopt)

```yaml
Policy LR:
  Min: 5.0e-7
  Best: 1.0e-6
  Max: 5.0e-6

Value LR:
  Min: 0.0005
  Best: 0.001
  Max: 0.002

LR Ratio (Value/Policy):
  Min: 100x
  Best: 1000x
  Max: 2000x
```

### Danger Zones

**❌ Policy LR too high (>5e-6)**:
- Symptom: Catastrophic forgetting, policy collapse
- Fix: Reduce to 1e-6 or lower

**❌ Value LR too low (<0.0005)**:
- Symptom: Explained variance <0.3, slow convergence
- Fix: Increase to 0.001

**❌ LR ratio <100x or >2000x**:
- Symptom: Loss stagnation, erratic training
- Fix: Maintain 1000x ratio

---

## Failed Experiment: Single LR

**Pod**: 0hczpx9nj1ub88 (2025-11-01)

```bash
# WRONG: Used single LR for both networks
train_ppo_parquet --learning-rate 0.001 --epochs 10000
```

**Result**:
- Loss **stagnated** at 1.158-1.159 after epoch 200
- Policy LR 1000x **too high** (0.001 vs hyperopt's 1e-6)
- Value LR **matched** hyperopt, but policy ruined convergence
- **Wasted**: ~40 minutes, $0.10

**Root Cause**: Policy network updated too aggressively, forgot previous good policies

---

## Monitoring Metrics

### Good Training (Dual LRs Working)

```
Epoch 50: policy_loss=0.342, value_loss=0.158, kl_div=0.002, expl_var=0.67
Epoch 100: policy_loss=0.198, value_loss=0.091, kl_div=0.001, expl_var=0.78
Epoch 150: policy_loss=0.134, value_loss=0.056, kl_div=0.0008, expl_var=0.84
```

**Indicators**:
- Policy loss **decreasing** smoothly
- Value loss **decreasing** faster than policy loss
- Explained variance **increasing** (>0.5 by epoch 50)
- KL divergence **low and stable** (<0.01)

### Bad Training (Single LR or Wrong Ratio)

```
Epoch 50: policy_loss=1.158, value_loss=1.159, kl_div=0.0, expl_var=0.21
Epoch 100: policy_loss=1.158, value_loss=1.159, kl_div=0.0, expl_var=0.20
Epoch 150: policy_loss=1.159, value_loss=1.158, kl_div=0.0, expl_var=0.19
```

**Red Flags**:
- Losses **stagnant** (no improvement)
- KL divergence **zero** (policy not updating)
- Explained variance **low and decreasing** (<0.3)
- **Action**: Stop training, fix learning rates

---

## Production Deployment

### Runpod Deployment (Corrected)

```bash
# deploy_ppo_production_corrected.sh
python3 scripts/runpod_deploy.py \
    --gpu-type "RTX A4000" \
    --image "jgrusewski/foxhunt-hyperopt:latest" \
    --command "train_ppo_parquet \
        --parquet-file /runpod-volume/test_data/ES_FUT_180d.parquet \
        --epochs 10000 \
        --policy-lr 0.000001 \
        --value-lr 0.001 \
        --batch-size 64 \
        --output-dir /runpod-volume/ml_training/ppo_production_\${TIMESTAMP} \
        --no-early-stopping"
```

**Expected**:
- Duration: 30-90 minutes
- Cost: $0.12-$0.38 @ $0.25/hr
- Output: Converged model with explained variance >0.7

---

## Verification Tests

### Local Test (5 epochs, ~30 seconds)

```bash
./target/release/examples/train_ppo_parquet \
    --parquet-file test_data/ES_FUT_180d.parquet \
    --epochs 5 \
    --policy-lr 0.000001 \
    --value-lr 0.001 \
    --batch-size 64 \
    --output-dir /tmp/ppo_test_dual_lr
```

**Success Criteria**:
1. Logs show "Policy learning rate: 0.000001"
2. Logs show "Value learning rate: 0.001"
3. Checkpoint files created in `/tmp/ppo_test_dual_lr/`
4. Training completes without errors

### Integration Test

```bash
cd /home/jgrusewski/Work/foxhunt
cargo test --release -p ml test_ppo_separate_learning_rates
```

**Checks**:
- PpoHyperparameters accepts `actor_learning_rate` and `critic_learning_rate`
- PPOConfig conversion preserves separate LRs
- Optimizers initialized with correct LRs

---

## Troubleshooting

### Issue 1: Loss Stagnation

**Symptom**:
```
Epoch 200: policy_loss=1.158, value_loss=1.159 (no change for 100+ epochs)
```

**Diagnosis**: Policy LR too high

**Fix**:
```bash
# Reduce policy LR by 10x
--policy-lr 0.0000001 --value-lr 0.001
```

### Issue 2: Explained Variance Low (<0.3)

**Symptom**:
```
Epoch 100: expl_var=0.21 (should be >0.5)
```

**Diagnosis**: Value LR too low or insufficient training

**Fix**:
```bash
# Increase value LR by 2x
--policy-lr 0.000001 --value-lr 0.002 --epochs 200
```

### Issue 3: Catastrophic Forgetting

**Symptom**:
```
Epoch 30: mean_reward=0.45
Epoch 50: mean_reward=-0.12 (suddenly negative)
```

**Diagnosis**: Policy LR too high

**Fix**:
```bash
# Reduce policy LR to minimum safe value
--policy-lr 0.0000005 --value-lr 0.001
```

### Issue 4: Slow Convergence

**Symptom**:
```
Epoch 500: value_loss=0.8 (still high after many epochs)
```

**Diagnosis**: Both LRs too low

**Fix**:
```bash
# Increase both LRs by 2x (maintain ratio)
--policy-lr 0.000002 --value-lr 0.002
```

---

## Code References

### train_ppo_parquet.rs (Lines 57-63)

```rust
/// Policy (actor) learning rate (default: 1e-6, ultra-conservative for stability)
#[arg(long, default_value = "0.000001")]
policy_lr: f64,

/// Value (critic) learning rate (default: 0.001, aggressive for faster convergence)
#[arg(long, default_value = "0.001")]
value_lr: f64,
```

### trainers/ppo.rs (Lines 74-96)

```rust
impl From<PpoHyperparameters> for PPOConfig {
    fn from(params: PpoHyperparameters) -> Self {
        // Use new separate learning rates if provided, otherwise fall back to defaults
        let policy_lr = params.actor_learning_rate.unwrap_or(1e-6);
        let value_lr = params.critic_learning_rate.unwrap_or(0.001);

        PPOConfig {
            policy_learning_rate: policy_lr,  // Actor learning rate
            value_learning_rate: value_lr,    // Critic learning rate
            // ... rest of config
        }
    }
}
```

### ppo/ppo.rs (Lines 698-732)

```rust
fn init_optimizers(&mut self) -> Result<(), MLError> {
    if self.policy_optimizer.is_none() {
        let policy_params = ParamsAdam {
            lr: self.config.policy_learning_rate,  // Separate LR for actor
            // ...
        };
        self.policy_optimizer = Some(Adam::new(self.actor.vars().all_vars(), policy_params)?);
    }

    if self.value_optimizer.is_none() {
        let value_params = ParamsAdam {
            lr: self.config.value_learning_rate,  // Separate LR for critic
            // ...
        };
        self.value_optimizer = Some(Adam::new(self.critic.vars().all_vars(), value_params)?);
    }

    Ok(())
}
```

---

## Changelog

### v1.0 (2025-11-01)

- ✅ Dual learning rate support implemented
- ✅ CLI flags added: `--policy-lr`, `--value-lr`
- ✅ Hyperopt validation: 63 trials, 14.3 minutes
- ✅ Best parameters identified: Policy=1e-6, Value=0.001
- ✅ Production deployment script updated
- ✅ Integration tests added
- ✅ Documentation created

### Historical Issues (Pre-v1.0)

- ❌ Single `--learning-rate` flag (deprecated)
- ❌ Loss stagnation at 1.158-1.159 (Pod 0hczpx9nj1ub88)
- ❌ Comments claimed binary limitation (false alarm)

---

## References

1. **Hyperopt Results**: `PPO_PARAMETERS_QUICK_REF.md`
2. **Deployment Scripts**: `deploy_ppo_production_corrected.sh`
3. **CLAUDE.md**: Lines 1-70 (Recent Updates section)
4. **Failed Attempt**: Pod 0hczpx9nj1ub88 (2025-11-01)

---

**Last Updated**: 2025-11-02
**Maintainer**: Claude Code (Anthropic)
**Status**: Production Ready ✅