SFC-ABM Core Engine

Stock-Flow Consistent Agent-Based Model engine for studying phase transitions in AI-driven labor market automation. Powers all five papers in the complexity-econ series (40,000+ Monte Carlo simulations).

What it does

Simulates 10,000 heterogeneous firms across 6 sectors (GUS 2024 calibration) interacting on a configurable network topology over 120 months. Firms decide whether to adopt AI, go hybrid, or stay traditional based on profitability thresholds, network mimetic pressure, and sector-specific CES elasticity of substitution (σ). A BDP (basic disposable payment) shock at month 30 triggers the automation transition.

Every monetary flow is tracked bilaterally: government taxes and spends, banks lend and absorb losses, the central bank sets rates via Taylor rule, and the exchange rate floats via balance-of-payments (PLN) or stays fixed under SGP fiscal constraint (EUR).

Architecture

src/main/scala/sfc/
├── Main.scala                    Entry point + Monte Carlo orchestrator
├── config/
│   └── SimConfig.scala           40+ parameters, 2 regimes, 4 topologies, env var overrides
├── agents/
│   ├── Firm.scala                TechState (Traditional→Hybrid→Automated→Bankrupt), decision logic
│   ├── Household.scala           Aggregate household state
│   └── CentralBank.scala         NBP/ECB rate wrapper
├── engine/
│   ├── Simulation.scala          Monthly step: labor → demand → firms → bank → inflation → forex → fiscal
│   └── World.scala               Immutable world state (macro + per-sector σ vector)
├── dynamics/
│   ├── SigmaDynamics.scala       Endogenous σ evolution (Arthur-style learning-by-doing)
│   └── DynamicNetwork.scala      Death-birth rewiring with preferential attachment
├── networks/
│   └── WattsStrogatz.scala       WS, Erdos-Renyi, Barabasi-Albert, ring lattice generators
└── sfc/
    └── BalanceSheet.scala        GovState, BankState, ForexState (SFC accounting)

Key features

Monetary regimes

• PLN: Floating exchange rate, endogenous NBP Taylor rule (α=1.5, β=0.8, inertia=0.70)
• EUR: Fixed rate at 4.33 PLN/EUR, exogenous ECB Taylor rule, SGP fiscal constraint (3% deficit, 60% debt ceiling, austerity κ=2.0)

Network topologies

• Watts-Strogatz small-world (k=6, p=0.10) — default
• Erdos-Renyi random graph
• Barabasi-Albert scale-free (preferential attachment)
• Ring lattice (no rewiring)

Firm decision logic

• 4-state technology transition: Traditional → Hybrid → Automated (+ Bankrupt)
• Profitability threshold via CES elasticity: θ = min(1.0, 0.88 + 0.075·log₁₀(σ))
• Network mimetic pressure: 40% weight on neighbors' adoption + 40% global panic
• Uncertainty discount reduced by demonstration effect (neighbors already automated)
• Sector-specific digital readiness, failure rates, and hybrid worker retention

Endogenous dynamics (Paper-05)

• σ evolution: σ(t+1) = σ(t) + λ·σ(t)·adoption(t)·(1 - σ(t)/cap) with ratchet + hard cap
• Network rewiring: bankrupt firms replaced with probability ρ, new entrants wire via preferential attachment
• Both disabled by default (λ=0, ρ=0) — backward compatible with Papers 01–04

Macroeconomic channels

• Phillips curve inflation (demand-pull + cost-push + import + tech-deflation)
• Soft deflation floor at -1.5%/mo (Bewley 1999 wage rigidity)
• Banking sector with NPL tracking, CAR constraint, endogenous lending rates
• Balance-of-payments forex with IRP arbitrage (PLN) or fixed rate (EUR)
• Government fiscal balance with SGP constraints (EUR only)

Sectors (GUS 2024)

Sector	Share	σ (CES)	Digital readiness	Hybrid retain
BPO/SSC	3%	50.0	0.50	50%
Manufacturing	16%	10.0	0.45	60%
Retail/Services	45%	5.0	0.40	65%
Healthcare	6%	2.0	0.25	75%
Public	22%	1.0	0.08	90%
Agriculture	8%	3.0	0.12	85%

Usage

Prerequisites

• JDK 17+
• sbt

Run simulation

# BDP = 2000 PLN, 30 seeds, PLN regime
sbt "run 2000 30 baseline pln"

# EUR regime with SGP
sbt "run 2000 30 baseline eur"

# Fat JAR (faster, no sbt startup overhead)
sbt assembly
java -jar target/scala-3.5.2/sfc-abm.jar 2000 30 baseline pln

Environment variable overrides

# Network topology
TOPOLOGY=er java -jar sfc-abm.jar 2000 30 test pln       # Erdos-Renyi
TOPOLOGY=ba java -jar sfc-abm.jar 2000 30 test pln       # Barabasi-Albert
TOPOLOGY=lattice java -jar sfc-abm.jar 2000 30 test pln  # Ring lattice

# Custom σ per sector
SIGMAS="8.97,4.88,4.95,1.0,0.8,1.44" java -jar sfc-abm.jar 2000 30 test pln

# σ multiplier (all sectors)
SIGMA_MULT=2.0 java -jar sfc-abm.jar 2000 30 test pln

# System size
FIRMS_COUNT=1000 java -jar sfc-abm.jar 2000 30 test pln

# Decision rule tuning
DEMO_THRESH=0.25 java -jar sfc-abm.jar 2000 30 test pln

# Endogenous σ (Paper-05)
SIGMA_LAMBDA=0.02 java -jar sfc-abm.jar 2000 30 test pln

# Dynamic network (Paper-05)
REWIRE_RHO=0.1 java -jar sfc-abm.jar 2000 30 test pln

# Full endogenous (both mechanisms)
SIGMA_LAMBDA=0.02 REWIRE_RHO=0.1 java -jar sfc-abm.jar 2000 30 test pln

Output

CSV files written to mc/ (European format: semicolon separator, comma decimals):

• mc/<prefix>_terminal.csv — per-seed terminal values at month 120 (26 columns)
• mc/<prefix>_timeseries.csv — aggregated time series (mean, std, p05, p95)

26 output columns: Seed, Inflation, Unemployment, TotalAdoption, ExRate, MarketWage, GovDebt, NPL, RefRate, PriceLevel, AutoRatio, HybridRatio, 6× sector adoption, EffectiveBDP, 6× sector σ, MeanDegree

Tests

93 tests across 8 suites, run on every push via GitHub Actions:

sbt test

Suite	Tests	Covers
FirmSpec	14	Tech states, worker counts, capacity, σ threshold
SimConfigSpec	12	Sector calibration, parameter bounds, regime detection
NetworkSpec	10	WS/ER/BA/lattice degree, symmetry, connectivity
BalanceSheetSpec	10	NPL ratio, CAR, lending rate, credit constraint
SimulationSpec	12	Labor market, inflation channels, Taylor rules
SigmaDynamicsSpec	6	Learning-by-doing, ratchet, cap, backward compat
DynamicNetworkSpec	6	Death-birth, preferential attachment, backward compat
IntegrationSpec	23	End-to-end: 120×26 output, reproducibility, bounds

Tech stack

• Scala 3.5.2 / sbt
• Zero runtime dependencies (stdlib only)
• ScalaTest 3.2.19 for unit tests
• sbt-assembly for fat JAR packaging

Papers using this engine

#	Paper	Sims	DOI
1	The Acceleration Paradox	6,300	10.5281/zenodo.18727928
2	PLN vs EUR with SGP	1,260	10.5281/zenodo.18740933
3	Empirical σ Estimation	120	10.5281/zenodo.18743780
4	Phase Diagram & Universality	18,540	10.5281/zenodo.18751083
5	Endogenous Technology & Networks	10,080	10.5281/zenodo.18758365

Citation

See CITATION.cff

License

MIT