provider-simenv

Agent-based supply chain simulation for the PROVIDER research project (BMBF-funded, OFFIS e.V.).

Models the global soya supply chain from Brazilian/US farms through wholesalers, sea transport, EU processors, and feed manufacturers to EU livestock farms. Scenarios apply KG-derived shock parameters (drought, port capacity, input price shocks) and observe emergent price and sourcing behaviour across the chain.

Built on Melodie (Python ABM framework).

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Project Structure

simenv/
├── pyproject.toml
└── src/
    └── provider_simenv/
        ├── main.py               ← entry point
        ├── model.py              ← simulation orchestrator
        ├── scenario.py           ← all scenario parameters
        ├── environment.py        ← global state + price aggregation
        ├── data_collector.py     ← Melodie output registration
        ├── tick_writer.py        ← per-tick PostgreSQL writer
        ├── db_config.py          ← PostgreSQL connection config
        ├── visualize_sql.py      ← plots from SQLite (post-run)
        ├── visualize_csv.py      ← plots from CSV (fallback)
        ├── agents/
        │   ├── farmer.py         ← BRA / USA / EU farmers
        │   ├── trader.py         ← wholesalers + feed traders
        │   ├── transport.py      ← land + sea transport operators
        │   └── process.py        ← processors + feed manufacturers
        └── data/
            ├── input/
            │   └── SimulatorScenarios.csv   ← scenario definitions
            └── output/                      ← generated at runtime
                ├── Result_Simulator_*.csv
                ├── provider-simenv.sqlite
                ├── price_curves.png
                └── volume_flow.png

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Dependencies

Python: 3.10 or higher

Required:

Melodie>=0.6.0
pandas
numpy
matplotlib
pyyaml

Optional — only needed for PostgreSQL output:

sqlalchemy
psycopg2-binary

If sqlalchemy / psycopg2-binary are not installed, the tick writer disables itself silently and the simulation continues normally. CSV and SQLite outputs are unaffected.

Install

# Create and activate a virtual environment
python -m venv .venv

# Windows
.venv\Scripts\activate

# macOS / Linux
source .venv/bin/activate

# Install core dependencies (run in project root)
pip install .

# Optional: Install all packages needed for development (run in project root)
pip install '.[dev]'

# This should ususally be done in editable mode for development purposes:
pip install -e '.[dev]'

# Optional: Install with PostgreSQL support (run in project root)
pip install '.[db]'

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Running the Simulation

# Navigate to the simulation package — Melodie resolves data/ paths from here
cd src/provider_simenv

# Run
python main.py

The simulation reads scenarios from data/input/SimulatorScenarios.csv, runs all scenarios in sequence, and writes output to data/output/.

What runs automatically:

1. Simulation loop — all scenarios, 52 steps each, per-tick stdout
2. Per-tick PostgreSQL writes via tick_writer.py (if Postgres is reachable; silent skip otherwise)
3. Post-run: CSV → SQLite merge → provider-simenv.sqlite

Generate Plots (after a run)

# From src/provider_simenv/

# Recommended: plots from SQLite — price curves + BRA/USA volume flow
python visualize_sql.py

# Fallback: plots from CSV
python visualize_csv.py

Output PNGs are saved to data/output/.

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Scenarios

Scenarios are defined in data/input/SimulatorScenarios.csv. Each row is one scenario run.

Parameter	Effect
farm_capacity_bra	BRA farm output multiplier — 1.0 = normal, 0.7 = 30% drought loss
port_capacity_sa	SA export port throughput multiplier
fertilizer_price_factor	Multiplier on BRA farmer fixed costs (GTA Red interventions)
energy_price_factor	Multiplier on all transport fixed costs
oil_mill_capacity	EU processor output multiplier
feed_mill_capacity	Feed manufacturer output multiplier
shock_onset_step	Step at which shock starts ramping in
shock_ramp_steps	Steps to ramp from baseline to full shock value
wholesaler_storage_capacity	Max tonnes a wholesaler can hold per step (default: 20 000 t)
usa_surplus_factor	USA idle capacity multiplier — 1.5 = 50% reserve above base yield
period_num	Number of simulation steps (default: 52)

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PostgreSQL Setup (Optional)

PostgreSQL enables live data access during the simulation — required for future palaestrAI integration. Without it, everything works via CSV + SQLite.

Start a local instance with Docker

docker run --name provider-postgres -e POSTGRES_PASSWORD=postgres -e POSTGRES_USER=postgres -e POSTGRES_DB=provider_simenv -p 5432:5432 -d postgres:16

These credentials match the defaults in db_config.py. No further configuration needed.

To persist data across container restarts, add a volume:

docker run --name provider-postgres -e POSTGRES_PASSWORD=postgres -e POSTGRES_USER=postgres -e POSTGRES_DB=provider_simenv -p 5432:5432 -v pgdata:/var/lib/postgresql/data -d postgres:16

Connection defaults (db_config.py)

Field	Default
host	localhost
port	5432
dbname	provider_simenv
user	postgres
password	postgres

Override by constructing PostgresDBConfig with different values or passing env vars at runtime.

Verify data after a run

-- Should return 3 rows, each COUNT = 52 (for a 3-scenario, 52-step run)
SELECT id_scenario, COUNT(*)
FROM "Result_Simulator_Environment"
GROUP BY id_scenario
ORDER BY id_scenario;

Tables written by tick_writer

Result_Simulator_Environment
Result_Simulator_BraFarmers
Result_Simulator_UsaFarmers
Result_Simulator_Wholesalers
Result_Simulator_Processors
Result_Simulator_FeedManufacturers
Result_Simulator_FeedTraders
Result_Simulator_EuFarmers

Tables are dropped and recreated at the start of each full simulation run (first scenario only). Subsequent scenarios within the same run append to the existing tables.

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Output Files

File	Description
data/output/Result_Simulator_*.csv	Raw per-agent per-step output written by Melodie
data/output/provider-simenv.sqlite	All CSVs merged into one SQLite database (post-run)
data/output/price_curves.png	Soja + feed price development across all scenarios
data/output/volume_flow.png	BRA vs USA sourcing volumes per scenario

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Known Issues / Notes

• Run from src/provider_simenv/ — Melodie resolves data/ paths relative to the working directory. Running from the repo root will fail to find input files.
• Melodie SQLite mode is disabled — data_output_type="sqlite" silently drops all rows due to a missing conn.commit() in SQLAlchemy 2.0. The csv_to_sqlite() function in main.py is used instead and called automatically.
• run_stepwise() in model.py is the designated integration hook for external control (e.g. palaestrAI). It yields a state dict {step, shock_scale, soja_price, feed_price, ...} after every simulation step.

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Project

PROVIDER — AI-based supply chain resilience simulation
OFFIS e.V. – Institut für Informatik, Oldenburg
BMBF-funded