Inflation

A simulation of how societies, power, debt and money arise, built up from late stone-age groups. The design brief lives in the project's Claude Doc. The repository holds the physical world, its plants and animals, and stone-age bands.

The world

inflation.world generates a region 1000 km wide and 2000 km from north to south on a 1 km grid (two million cells), spanning about 45°N to 27°N, the latitudes from the Black Sea and the Balkans down to northern Arabia and Sinai: cold continental and alpine in the north, hot and dry in the south. Latitude follows distance (1° per 111 km), so smaller test maps span fewer degrees around 36°N. The region is one continent-like mass running through every latitude band, with offshore islands and ocean on every side. --size KM makes a square map, and --height KM sets its north–south extent.

Generated once

Layer	Model
Tectonics	About 14 plates per million km² on a warped Voronoi map, 60% continental, chosen nearest the centre against the map's own proportions so land runs its full length. Continental crust varies in thickness and is thickest in the old core, so drowned shelves and inland seas lie mostly on the margins. Collisions raise mountain belts; rifts open valleys with lakes or a narrow gulf (at most 900 m deep), not open ocean. Ocean floor deepens with distance from spreading ridges (2.5 to 4.5 km); oceanic plates sinking under others leave trenches. A band along every edge is ocean floor
Volcanoes	Arcs in a line 105–135 km behind trenches where the plates close fast (continental arcs or island arcs), hotspot chains that age along the plate's motion (active shield at one end, drowned seamounts at the other), and rift cones. Old edifices are eroded with the land, young ones are built afterwards
Erosion and sediment	Stream-power law (implicit Braun & Willett 2013 solver, 40 steps × 50,000 years) and hillslope diffusion. Eroded material is carried downstream: rivers drop what exceeds their capacity, closed basins fill, large rivers build delta plains, and the rest builds a sloping shelf out to a shelf break
Geology	Rock type per cell (sets erodibility and soil), sediment thickness; flint, clay, obsidian, ochre, salt, copper, tin, bitumen
Climate	Monthly normals: latitude, 6.5 °C/km lapse rate, continentality; moisture carried from every sea along each weather regime's wind, fronts in a storm track under the jet, orographic rain and rain shadows; Mediterranean dry summers in the south
Rivers and lakes	Thornthwaite evapotranspiration, Fu–Budyko runoff, D8 routing; lakes from a water balance, closed basins turn saline. Valley floors are planed flat beside rivers (width grows with the square root of discharge). Rivers are classed creek, stream, river and great river; reaches with a third of a metre of water and no rapids are navigable by canoe or raft
Floodplains	Height above the nearest river (HAND); land a large flood (about ten times mean flow) reaches is floodplain
Terrain	Ruggedness from slope, local relief and a rock roughness the 1 km grid cannot resolve (lava fields and karst roughest, alluvium smoothest, buried under thick sediment). Walking effort from Tobler's hiking function, roughness, wetlands and river crossings. A river is a sub-cell channel, not a 1 km strip of water: its cost comes from this week's depth (knee deep a wade, waist deep slow, past chest deep a swim most animals refuse), and wide braided reaches on gentle ground have fords while gorges run deep. A stream in spate stops animals on foot; in the dry season the same river can be crossed. Open water is impassable on foot. Line of sight over the terrain in 16 directions out to 30 km with earth curvature; prominence over the surroundings; defensibility from height, broken ground and approaches cut by water, marsh or steep slopes
Biomes	Potential vegetation from aridity, temperature and drainage, including marsh, swamp forest, bog, salt marsh, mangrove and floodplain forest

The hex world

The world moves on 10 km hexes summarised from the 1 km grid (HexMap, HexWorld). Each hex is split into height bands (below 500 m, 500–1000, 1000–1500, 1500–2500 and above); a band of a hex is a place, about 23,000 on the full map. Borders between hexes carry the effort of crossing them by way of travel (walking, climbing, laden, swimming), with rivers on the hex edges graded by depth at the best crossing, and cliffs and gorges from the fine terrain. Weather, water and plants run per place (HexLand).

Animals (inflation.ecology):

Layer	Model
Soil and small life (HexSmallLife)	Litter, organic matter and soil animals; carrion rotting by warmth; plant-eating and biting insects, rodents, reptiles and amphibians, pollinators setting the fruit crop; hares, rock hyrax, six wild birds (quail and greylag geese migrate), tortoises, foxes and wildcats; golden eagles on crags; griffon vulture colonies soaring 80 km for carcasses
Residents (HexFauna)	Densities per place for every plant-eater and for the hunters that keep to small home ranges: grazing shared by diet, forage quality, water within reach, crowding disease, shifts between height bands, spill to neighbouring hexes
Packs (HexGroups)	The hunters as groups that plan a week's walk over the hexes and hunt the residents; meetings on the way are timetabled and settled in order (hunters rob or kill weaker ones, rival packs give way or fight); territories, thirst, hiding in cover, moonlight, seasonal memory
People (HexPeople, HexCulture, HexRoutes)	Bands that choose each week where to camp and set their ways: effort on each food, stores that spoil, tools, clothes and shelters made from materials, firewood, night fires, raids; skills held by members and split with them; traditions, ties between bands, a shared naming language, remembered places, and routes told by landmarks
Sense of direction (HexBearings)	Each month every kind knows the country within 60 km and the peaks it can see out to 200 km, and feels which way is cooler or warmer when the month is wrong for its coat; groups far out of their country trek that way

What is ported from the earlier 1 km model and what is not is in docs/design/hex-port-status.md.

Over time on the fine grid

The fine grid's own weekly weather, water and plants (Weather, LiveWater, Vegetation) are kept as the reference the hex versions are checked against (HexLandCheck, HexWeatherCheck). One step is 6 days (5 steps per month), configurable in WorldConfig.

Process	Model
Calendar	12 months × 30 days; the moon is new on day 1 and full on day 16; the year starts at the winter solstice (month 1 about January) and a run at the spring equinox; day length by latitude
Weather	Weekly weather regimes with their winds: westerly fronts, cold northerly outbreaks, warm southerlies, blocking highs, and the summer high with steady north winds over the south. The jet stream lies over the north in summer and moves south in winter, meandering week to week. Rain falls on the slopes facing the week's wind, with rain shadows behind ridges and volcanoes, and still averages to the normals. The wind drives fire spread, ash plumes and sea upwelling, and is known a week ahead. On top of that: coarse autoregressive temperature and rain anomalies (about five days' persistence), wet and dry years, a quasi-periodic ~5-year oscillation and a decadal swing with their own spatial patterns. Shocks: drought years over a region (12% chance a year somewhere), multi-year droughts (about 1.5% chance a year), severe winters (6%), heat waves (8%), and volcanic winters after VEI 5+ eruptions. Snowpack with degree-day melt; on the hexes, snow deeper than a glacier there can stand (ice yielding at 100 kPa on its bed: Nye) flows as ice to the next place down and melts there, or off the land at the sea.
Water	Soil bucket (150 mm), groundwater and baseflow; runoff routed down the network every step. Rivers above bankfull (4× mean) flood their floodplains
Waterworks	Dams with reservoirs that fill and release steadily, canals that divert part or all of a river (must run downhill and cannot loop), irrigation onto fields, and permanent rerouting of a river
Eruptions	Active volcanoes erupt at their own rates; explosivity follows the VEI frequency distribution; ash falls downwind, smothers vegetation and enriches soil
Vegetation	Herbs, shrubs and trees per cell, growing towards a ceiling set by recent moisture, warmth and soil. They die back under drought, frost, deep floods, ash and fire, and regrow: herbs within a season, trees over decades and only from nearby seed. Grazing, browsing and felling go through consume; animals' passage through trample, which wears trails

Learned behaviour (inflation.learning)

Every choice a group makes (where to go each week, and its ways: effort on each food, stores, what to make) has a hand-written rule, and can instead be made by a small network (Mlp, plain Kotlin, no dependencies). There are move networks by role (Role): one for the hunters and one for people; kinds within a role share it and are told apart by their traits and a learned identity. Bands' ways have a network of their own (ways.mlp).

• HexPpo trains them by proximal policy optimisation: each round, training worlds with all the animals and people run on the current networks, a share of every kind's choices is recorded, and each choice is judged by what became of the group's members over the following weeks (Outcomes, Critic). Every few rounds each role's new network is set against its kept one on a settled test world (EcoCheck, keys ppo.check*) and kept only if the whole ecosystem holds up (kept/). Command line: PpoOptions.USAGE; learning settings are ppo.* keys.
• HexEvolveWays evolves bands' or packs' ways by evolution strategies (keys evolveWays.*).
• HexPickWorld ranks small worlds by how hard their seasons push plant-eaters to move.

A network is saved with a .names file listing its inputs and outputs, so it keeps working as features are added (Schema, docs/design/model-compatibility.md). nets=DIR in the config file makes the networks in DIR the model for any run (LearnedModel); without it the hand-written rules are the model.

Running

Requires Gradle 9 (the wrapper is included); a JDK 21 toolchain is downloaded if it is missing.

./gradlew test
./gradlew run --args="--seed 7 --out output/seed7"
./gradlew hexViewer -PviewerArgs="--seed 1"
./gradlew hexFauna -PfaunaArgs="--seed 1 --years 10"
./gradlew runTool -Pmain=inflation.tools.WindReportKt -PtoolArgs="--seed 1"   # any tool, by its main class
./gradlew hexPpo -PppoArgs="--out runs/ppo --size 2000 --rounds 20"           # the trainer

Every tool, what it answers and how to run it: docs/tools.md.

run writes PNG maps (relief, biomes, geology, minerals, sediment, rivers, precipitation, temperature, soil) and summary.txt, including snow cover from three simulated years. --size 400 makes a smaller region.

hexViewer opens the hex world over the fine terrain with time controls; packs and bands glide from hex to hex, tints show weather, water, plants, small life and residents, arrows show the wind or a kind's sense of direction, and clicking a hex lists everything living there. Picking a group in the list and pressing Follow… opens the follow window: its local map (the country a band does not know dimmed, its way over the last four weeks, the pull of its round or season's place), how it stands and who shares its hex, what it knows of itself and of each place it can reach, the places coloured by how the model scores them with the model's pick in yellow, and its ways for the week. Click another place or pin a way to override the model; Next step runs the week, and the next week then waits at the group's choice (unless "Model decides" is ticked). The overview's Run and Step take over: their weeks run on the model's choices. nets=DIR, with ways=FILE, in the config file makes the learned networks the model, as in hexFauna; without them it is the hand-written choices.

hexFauna runs the hex world for some years and prints each kind's numbers, the small life, the causes of death and the cost of a step, and for people a line against the ethnographic record (band size, density, camp moves, ground walked, plant share of food, birth spacing, children reaching 15, years left at 15, violent deaths). uniformStart=true in the config file starts every kind spread evenly over the land; people=false in the config file leaves people out, for comparison; huntDiag=KIND traces hungry and thirsty groups of a kind.

Run settings other than seeds, years and sizes are keys in a config file, not switches: inflation.properties in the directory the run starts in (the project directory for the Gradle tasks), or the file -Dhex.config=FILE names. config.example.properties lists every key with its default. A mechanic that has replaced an older way gets no key to bring the old way back; keys are kept for what runs really vary: the networks and paths, features that can be switched (rounds, taming), and tuning values (t.*).

A running world can be saved and carried on after small changes to the code: --save FILE (every five years and at the end) and --load FILE in hexFauna, Save…/Load… and --load FILE in the viewer. Fields are matched by name, so a field added since keeps its fresh value and one removed is dropped. The generated world itself is kept in ~/.inflation/world-cache and loaded in seconds while the world-generating code and settings are unchanged (worldCache=false turns this off).

Short tests start from settled test worlds rather than from year 0, so they see a change's effect and not the first years' swings. ./gradlew testWorld -PtestArgs="build full-1 full-2 full-3" runs each of the three full-map seeds for 30 years (--years N) under the config file's keys and keeps it in ~/.inflation/test-worlds; testWorld -PtestArgs="list" shows what is built and from which commit. A change is tested with testWorld -PtestArgs="ab --variant change.properties": the base and the variant (the change's keys laid over the base config) run for 3 years on each full map, twice with the weather drawn differently (--years, --replicates, --parallel, --worlds), and the report gives each kind's effect paired by weather, the base's own swing with the weather, and whether every pair went the same way. A settled world still drifts, so a change is never judged against older numbers, only against its base. Smaller maps do not track the full map (see TestWorlds.kt); small-1 is for checking that code runs. hexFauna --world NAME --years N [--replicate R] carries one settled world on by itself.

Every hexFauna run ends by saying whether it stayed within nominal limits (run/Nominal.kt): wide bounds on every series of its history (numbers that are numbers, matter not below zero, fed within 0..1, weather and densities in reason, no kind gone, no kind or stock swinging many times over from year to year, each kind's births and deaths adding up to the heads it gained, hunters fed, holding ground and killing, hunters against the hunted by biomass, and bands keeping at least what the Natufians had: fire, spears, clothes, hunting and game in their food) and on the state it ends in (every table of the weather, land and animals a number, every stock at or above zero, shares within 0..1, groups sound, the books if kept). testWorld ab reports the same for each run and what the variant alone broke, the training's ecosystem check adds a line for its runs and logs each training world's state as it is replaced, and testWorld -PtestArgs="nominal HISTORY.csv..." checks histories already made. It is reported only, and its limits are set from reference values in nature, with their sources in the code.

Known simplifications

• Rivers use single-direction (D8) routing, randomised during erosion to avoid parallel channels.
• Within a 6-day step, water reaches the river mouth at once, so flood peaks on large rivers come early and sharp. Daily temperature extremes are averaged away, which understates lowland snow days.
• There is no monsoon.
• Vegetation starts from the long-term climate and takes decades of simulated time to settle; forests advance only from neighbouring forest.
• Volcanic cones are idealised shapes with noise; lava flows are not modelled, only ash.
• The herbivores' food supply (shares of standing herbs, shrubs and trees for each kind of food) is a set of calibration constants, not derived from plant physiology.
• The moon's cycle is exactly 30 days to keep months and moons aligned (the real one is 29.53).