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PEP-003: Engine

Field Value
PEP 003
Title Engine
Status Draft
Author PEP Working Group
Created 2026-03-22

Abstract

This specification defines the Engine, the orchestrator of the evolutionary process. An engine manages a population of organisms through generations using configurable selection, crossover, mutation, and termination strategies.

Motivation

The engine is the control plane of evolution. Standardizing its configuration enables reproducible experiments, composable pipelines, and interoperable tooling. Different selection pressures, crossover methods, and termination conditions can be swapped declaratively.

Specification

Top-Level Fields

Field Type Required Description
id UUID Yes Unique identifier
name string Yes Engine name (1-128 chars)
version string Yes Semantic version
population object Yes Current population state
selection object Yes Selection strategy configuration
crossover object Yes Crossover configuration
mutation object Yes Mutation configuration
termination object Yes Stopping conditions

population Object

Field Type Constraints Description
size integer > 0 Target population size
organisms array[UUID] — Current organism IDs
generation integer >= 0 Current generation number

selection Object

Field Type Constraints Description
strategy enum — "tournament" | "roulette" | "rank" | "elite"
pressure float [0, 1] Selection pressure
elitism_rate float [0, 1] Fraction preserved unchanged

crossover Object

Field Type Constraints Description
method enum — "single_point" | "two_point" | "uniform" | "none"
rate float [0, 1] Probability of crossover per pair

mutation Object

Field Type Constraints Description
rate float [0, 1] Probability of mutation per gene
decay float [0, 1] Rate at which mutation rate decreases

termination Object

Field Type Constraints Description
max_generations integer > 0 Hard limit on generations
fitness_target float [0, 1] Stop when best fitness reaches this
stagnation_limit integer > 0 Stop after N generations without gain

Example

{
  "id": "d4e5f6a7-b8c9-0123-def0-456789abcdef",
  "name": "main-evolver",
  "version": "3.0.0",
  "population": {
    "size": 200,
    "organisms": [],
    "generation": 0
  },
  "selection": { "strategy": "tournament", "pressure": 0.75, "elitism_rate": 0.05 },
  "crossover": { "method": "two_point", "rate": 0.85 },
  "mutation": { "rate": 0.02, "decay": 0.005 },
  "termination": { "max_generations": 1000, "fitness_target": 0.99, "stagnation_limit": 100 }
}

Conformance Requirements

  1. population.size MUST be > 0.
  2. All organism IDs in population.organisms MUST be valid UUIDs.
  3. All float fields with range [0, 1] MUST be enforced.
  4. termination.max_generations and termination.stagnation_limit MUST be > 0.
  5. Enum values MUST match exactly (case-sensitive).

References