Decision Points
When to Use Single vs. Cascaded Evaluators
Problem characteristics:
├── Search space tractable (b^d < 10^9)
│ └── Use single best evaluator → standard optimization
└── Search space intractable (b^d > 10^12)
├── Uniform evaluation budget available
│ └── Use cascading approximation:
│ 1. Fast pruning (policy network) → narrow beam
│ 2. Medium evaluation (value network) → estimate quality
│ 3. Cheap exploration (rollouts) → breadth coverage
└── Non-uniform evaluation budget
└── Adaptive allocation:
├── Critical positions → expensive evaluation
└── Routine positions → cheap heuristics
Accuracy vs. Latency Requirements Decision Tree
System requirements:
├── Latency critical (<1ms response)
│ ├── Accuracy tolerance high (>10% error acceptable)
│ │ └── Fast rollouts only (2µs/evaluation)
│ └── Accuracy tolerance low (<5% error)
│ └── Cached policy network + heuristic fallback
├── Latency moderate (1-100ms response)
│ ├── High accuracy needed
│ │ └── Value network (3ms) + policy network guidance
│ └── Balanced accuracy/speed
│ └── Mixed evaluation: λ=0.5 value + rollouts
└── Latency tolerant (>100ms)
└── Full cascade: policy → value → rollouts with MCTS
Error Mode Diversity Assessment
When choosing multiple evaluators:
├── All evaluators have similar failure modes
│ └── Use single best evaluator (no diversity benefit)
├── Evaluators have complementary errors
│ ├── Fast/noisy + slow/accurate pairing
│ │ └── Mix at λ=0.3-0.7 (bias toward accurate)
│ ├── Conservative + exploratory pairing
│ │ └── Mix at λ=0.5 (equal weighting)
│ └── Learned + handcrafted pairing
│ └── Dynamic mixing based on confidence scores
└── Unknown error correlation
└── Empirical testing: measure performance on holdout set
Failure Modes
Schema Bloat (Detection: >5 approximation layers)
Symptom: Adding more approximation layers but seeing diminishing returns Root cause: Each layer adds overhead without proportional accuracy gain Fix: Profile computational cost vs. accuracy improvement; remove layers with poor ROI Detection rule: If adding layer N improves accuracy <5% but increases latency >20%, you have schema bloat
Synchronous Coupling (Detection: Fast components waiting idle)
Symptom: CPU utilization drops while waiting for GPU evaluation Root cause: Tight coupling between fast search and slow neural network evaluation Fix: Implement asynchronous queuing with stale value tolerance Detection rule: If fast components (search, rollouts) have >50% idle time, you have synchronous coupling
Proxy Metric Fixation (Detection: Metric improving but performance degrading)
Symptom: Move prediction accuracy improves but win rate decreases Root cause: Optimizing for human imitation instead of objective success Fix: Switch from supervised learning to reinforcement learning with true objective Detection rule: If proxy metric and outcome metric trend in opposite directions >10 evaluations, you have proxy fixation
Single Evaluator Fallacy (Detection: Rejecting "worse" individual components)
Symptom: Discarding rollouts because value network has higher individual accuracy Root cause: Assuming best individual component makes best system component Fix: Test mixture performance empirically; diversity often beats individual quality Detection rule: If you're selecting components by individual performance without testing combinations, you have single evaluator fallacy
Uniform Budget Allocation (Detection: Same computation for all decisions)
Symptom: Spending equal evaluation time on obvious moves and critical positions Root cause: Not adapting computational budget to decision importance Fix: Implement adaptive allocation based on position uncertainty and outcome sensitivity Detection rule: If evaluation time variance across positions <20% of mean, you have uniform allocation
Worked Examples
Implementing Cascading Approximation for Code Review
Scenario: Design AI system for reviewing pull requests with 50-500 changed lines, need <10s response time, must catch 95% of bugs.
Step 1: Analyze computational constraints
- Static analysis: 10ms per file
- ML bug detector: 2s per file
- Deep semantic analysis: 30s per file
- Available budget: 10s total
Step 2: Apply cascading decision tree Following "search space intractable" path since exhaustive analysis exceeds budget:
- Fast pruning layer (static analysis): Eliminate files with no complexity changes
- Medium evaluation layer (ML detector): Score remaining files for bug likelihood
- Expensive analysis layer (semantic): Deep dive on highest-scoring files only
Step 3: Budget allocation strategy
- Reserve 2s for ML evaluation of all remaining files
- Allocate remaining 8s to semantic analysis based on ML scores
- Files scoring >0.8: get 4s each (max 2 files)
- Files scoring 0.5-0.8: get 2s each
- Files scoring <0.5: get ML score only
Step 4: Mixture evaluation implementation Instead of using "best" evaluator (semantic analysis), mix ML + semantic scores:
- ML detector: fast, good at pattern matching, misses novel bugs
- Semantic analysis: slow, catches complex logic errors, high false positive rate
- Mixture at λ=0.6:
final_score = 0.6 * semantic + 0.4 * ml
Novice approach: Run semantic analysis on everything → timeout after first few files Expert insight: The cascade allows spending expensive compute only where it matters most, while ensuring every file gets some evaluation
Quality Gates
[ ] N evaluators tested: Minimum 3 evaluators with different speed/accuracy profiles implemented and benchmarked
[ ] Error correlation measured: Pairwise correlation matrix computed showing evaluators have <0.7 correlation on test set
[ ] Mixture vs. single evaluated: Empirical comparison showing mixture outperforms best individual component by >5%
[ ] Latency requirements met: 95th percentile response time under specified threshold with full cascade
[ ] Accuracy requirements met: Error rate on holdout set meets specified threshold (e.g., <5% false negative rate)
[ ] Budget allocation profiled: Computational cost breakdown shows budget distributed according to decision importance
[ ] Failure mode testing: System tested under adversarial conditions (distribution shift, resource constraints, edge cases)
[ ] Asynchronous coordination verified: Fast components maintain >80% utilization even when slow components are saturated
[ ] Scalability validated: Performance degrades gracefully when increasing load 10x beyond nominal capacity
[ ] Monitoring instrumentation: Metrics track proxy vs. outcome alignment, component utilization, and cascade effectiveness
NOT-FOR Boundaries
Do NOT use this skill for:
- Simple optimization problems with tractable search spaces → use standard-optimization instead
- Single-model training or tuning → use deep-learning-training instead
- Real-time systems requiring <1ms latency → use low-latency-systems instead
- Problems where one evaluator is clearly superior and others add no value → use single-model-deployment instead
- Sequential decision processes without search tree structure → use reinforcement-learning-fundamentals instead
Delegate to other skills when:
- Need to implement specific neural network architectures → deep-learning-architectures
- Designing distributed systems infrastructure → distributed-systems-design
- Optimizing individual component performance → performance-optimization
- Handling training data collection and labeling → data-engineering
- Implementing specific search algorithms → search-algorithms
This skill focuses specifically on: Architectural patterns for coordinating multiple imperfect evaluators under computational constraints, not the implementation details of individual components.