ReNunney/docs/TRACK2_PROGRESS.md

Track 2 Implementation Progress

Updated: 2026-04-12

Completed Components

1. Simulation State Model (simulation.rs)

• Config: Simulation configuration with parameters (K, N0, R, T, n, u, epochs, etc.)
• State: Snapshot of population/genotype at a generation
• TerminationReason: Termination conditions (MaxGenerations, Extinction, MissingSex, Success)
• Event: Events during simulation (PopulationChange, GenotypeChange, Extinction, GenerationComplete)
• RunResult: Result of a single run with extinction probability
• Tests: Config validation, termination reason display, survival/extinction probability

2. Extinction Probability Trait (extinction_trait.rs)

• ExtinctionEstimator trait: Interface for running simulations and estimating extinction probabilities
  • run() - Run a single simulation
  • estimate_extinction_count() - Count extinctions over multiple runs
  • estimate_extinction_probability() - Compute extinction probability
• FixedRunEstimator: Baseline estimator with fixed number of runs (default 20)
• AdaptiveEstimator: Dynamic estimator that adjusts runs based on confidence
• Tests: Estimator creation and defaults

3. Threshold Search Strategies (search.rs)

• ThresholdSearchStrategy trait: Interface for finding threshold T where P(extinction) = target
• BinarySearchStrategy: Simple binary search over T values
• BracketRefineStrategy: Binary search with refinement rounds
• SweepStrategy: Compute all T values for data table/plot generation
• Tests: Strategy creation and defaults

4. Orchestration I/O (io.rs)

• Track2Job: Job manifest for submitting Track 2 simulation jobs
• Track2Result: Result manifest with job status and summary
• Track2Summary: Compact run result summary
• Track2Error: Error details for failures
• Tests: Job creation, success/failure results

5. Simulation Kernel (simulation_kernel.rs)

• SimpleSimulationKernel: Deterministic placeholder for trait wiring
• NunneySimulationKernel: Minimal Nunney-style stochastic kernel for smoke comparisons
• Tests: Kernel creation, fecundity, fitness monotonicity, mutation bounds, inheritance, extinction, and bookkeeping invariants

6. Module Organization (lib.rs)

• All modules properly integrated
• Common types re-exported for easy access

7. Dependencies (Cargo.toml)

• serde with derive features
• rand for random number generation

Design Principles

1. Separation of concerns: Each module has a clear, single responsibility
2. Trait-based abstraction: ExtinctionEstimator and ThresholdSearchStrategy allow swapping implementations
3. Serialization-friendly: All core types are Serialize/Deserialize
4. Testable: Each component has unit tests
5. Clear documentation: Module-level docs explain purpose and usage

Testing Strategy

Each component can be tested independently:

1. Config: Just validation and derived calculations
2. ExtinctionEstimator: Tests of estimator creation and basic probability calculations
3. ThresholdSearchStrategy: Tests of strategy creation and basic search behavior
4. I/O: Tests of JSON serialization/deserialization
5. Simulation Kernel: Tests of kernel creation and deterministic behavior

Next Steps

1. Use the current Rust framework operationally through:
   • make rust-smoke
   • make rust-smoke-release
   • make compare-track1-rust-smoke
2. Tighten the remaining systematic differences from Python in births, survivors, and final population size.
3. Expand low-level kernel tests for hand-constructed tiny populations and exact metric expectations.
4. Define statistical parity targets over seed ranges and track them explicitly.
5. Promote the Rust kernel into a real Track 2 execution backend once the mechanics are stable enough.

Files to Copy

1. /tmp/track2-simulation.rs → rust/track2-core/src/simulation.rs
2. /tmp/track2-extinction-trait.rs → rust/track2-core/src/extinction_trait.rs
3. /tmp/track2-search.rs → rust/track2-core/src/search.rs
4. /tmp/track2-io.rs → rust/track2-core/src/io.rs
5. /tmp/track2-simulation-kernel.rs → rust/track2-core/src/simulation_kernel.rs
6. /tmp/track2-lib.rs → rust/track2-core/src/lib.rs
7. /tmp/Cargo.toml.new → rust/track2-core/Cargo.toml

Integration

After copying the files, run:

cargo check
cargo test

This will verify that all modules compile and all tests pass.