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doma.play

Setup

The main simulation (in /sim, included as a submodule) is implemented in Rust; you'll need to compile it first:

cd sim
cargo build --release

For the front end, install the NPM and Python packages:

npm install -d
pip install -r requirements.txt

Usage

  • Run redis-server.
  • npm start to start the frontend and API server, then go to localhost:8000 for the city view.
  • Run the simulation with ./sim/target/release/doma_sim. The API server will interface with this via Redis.

You can also view active player information at /play/players, useful for debugging.

Designer

Visit /design to access the map designer.

Basic usage:

  • Click to select a cell
  • Shift+click to add to the selection
  • Ctrl+shift & move mouse to paint selection
  • Click source to get map data
    • You can paste in map data here to "load" an existing map


Simulation design

Initialization

The city has a tenant population, who live in the city, and a set of landlords, who represent institutional property owners.

  1. Generate the city, based on the specified design
  2. Generate n tenants, with an income drawn from the specified distribution and a random work location drawn from commercial buildings
  3. Tenants decide where to move in, based on desirability and affordability. Tenants are on one year leases starting on a random month.
  4. Distribute properties randomly to tenants and landlords
    • If there are occupying tenants, a property has 1/3 chance of going to a landlord, 1/3 a chance of going to an occupying tenant, and 1/3 chance of going to a random tenant
    • If there are no occupying tenants, there's a 50/50 chance of it going to a landlord or a random tenant
  5. Generate a tenant social network. Each tenant is friends with 2 to 16 other random tenants. This social network is used for a word-of-mouth model.

Steps

Each step represents one month.

  1. Each unit's owner collects rent (if occupied).
  2. In random order, step through landlords. Each landlord:
    1. Estimates market rents for each neighborhood. The landlord looks at rents of occupied units they own as well as a random sample of occupied units in each neighborhood. The landlord saves the maximum values of these rents.
    2. These samples are also used to estimate a ratio of maintenance to rental income; the landlord adjusts their maintenance expenditures based on these samples (i.e. they estimate the minimum maintenance expenditure they can get away with).
    3. For each neighborhood, the landlord fits a line to the past 12 months of these maximum rent samples to estimate the rental trends for that neighborhood. This also lets them estimate the profit of purchasing that unit now (i.e. the different in its current rent vs its projected rent).
    4. Each of the landlord's units' conditions decay randomly, and then improve based on their maintenance expenditure.
    5. Lowers the rent of vacant units, multiplying the existing rent by 0.98 every two months.
    6. Increases the rent of occupied units with lease renewals. The rent is increased either by their estimate for the rent trends of that neighborhood, or by config.rent_increase_rate, whichever is higher.
    7. Decides what properties to make offers on. A random neighborhood is chosen, weighted by estimated profits for each neighborhood, and a random sample of 20 properties is chosen. An estimated value is calculated for that property, based on projected rent, and compared to the current value (based on current rent). If the estimated value is greater, an offer is made at the estimated value.
  3. In random order, step through tenants. Each tenant:
    1. Decides if they should move. If the tenant is homeless, they always look for an affordable option. Otherwise, they only look if they are between leases, or if their current rent is no longer affordable. In either case, they consider a random sample of vacant units and look for a unit that balances affordability and desirability (if the tenant has a current unit, a moving penalty is incorporated).
  4. If this month is the start of a new year, all units are appraised, using the mean of recent (past year) sale prices in that neighborhood. If there haven't been any sales, config.base_appreciation is used instead.
  5. DOMA:
    1. Collects rent from its tenants
    2. Pays dividends from this rent to its members
    3. Makes offers on properties. DOMA prioritizes non-DOMA properties of their members and cheap properties with high rent-to-price ratios. DOMA makes offers on as many properties as it can afford.
  6. All property owners check purchase offers. Tenants compare the offer to the last appraised value of the property, landlords compare to their own estimate of its value based on projected rent. They accept when the offer is greater than that value.

Key simplifying assumptions

  • We assume landlords have access to limitless capital
  • There is a point-to-point transit system for commutes
  • We don't include developers

Script notes

  • The script structure must be such that players hit the same checkpoints in the same order. This is because to proceed through a checkpoint, the server checks that all players have reached that checkpoint. If some players hit checkpoint A and others hit checkpoint B, the game can't progress further.
  • The scene id START is special; the scene with this id is sent as the first scene
  • If the next scene id is absent or null, then that is considered the end of the script, and the game will restart. The best way to setup an ending scene is to set a checkpoint, so that all players must arrive at the ending at the same time--that way, the game won't restart while other players are still finishing up.

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