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v0.6.0

Released 2026-05-13 · GitHub Release

Overview​

  • Add calculated parameters to model.parameters: a string value is treated as an arithmetic expression over other parameters and evaluated at simulation build time
  • Expose the largest eigenvalue of the contact matrix as a reserved parameter CONTACT_MATRIX_EIGENVALUE_ALL usable in calculated-parameter expressions
  • Regenerate population metadata to match the current upstream subnational naming (single-underscore → double-underscore)

Simulations​

POST /api/v1/simulations

Calculated parameters​

Values in model.parameters can now be expressions over the other parameters. Useful for branching outflow rates and for deriving one parameter from another:

{
  "parameters": {
    "p_h": 0.05,
    "gamma": 0.1,
    "alpha": 0.2,
    "recovery_rate": "(1 - p_h) * gamma",
    "hospitalization_rate": "p_h * alpha"
  }
}

Source-parameter shapes propagate via numpy broadcasting, so an age-varying or seasonally-scaled source flows through the expression automatically. Calculated parameters evaluate after parameter_transforms.

Expressions can only include strict arithmetic syntax: +, -, *, /, //, **, %, unary +/-, parentheses, numeric literals, and parameter names. No function calls, attribute access, subscripts, comparisons, or conditionals. Circular references and undefined names raise 422 with the offending name.

A calculated parameter cannot be the target_parameter of a parameter_transform. Apply the transform to a source parameter instead and let it propagate through the expression.

See the Parameters guide for the full description and examples.

Reserved name: CONTACT_MATRIX_EIGENVALUE_ALL​

The largest eigenvalue of the summed contact matrix (across all layers) is available as CONTACT_MATRIX_EIGENVALUE_ALL. The most common use is calibrating transmission_rate from a target R0R_0:

{
  "parameters": {
    "R0": 1.5,
    "gamma": 0.1,
    "recovery_rate": "gamma",
    "transmission_rate": "R0 * gamma / CONTACT_MATRIX_EIGENVALUE_ALL"
  }
}

User parameter names cannot collide with reserved names. Reserved values are injected only into the expression namespace; they do not appear in results.parameters.

Populations​

GET /api/v1/populations

Population name identifier update​

A recent epydemix-data v1.2.0 update switched subnational identifiers from a single-underscore to a double-underscore separator (e.g. United_States__Massachusetts rather than United_States_Massachusetts). The precomputed population metadata CSVs (app/data/population_metadata.csv and app/data/population_age_distribution.csv) have been regenerated against the current release to match.

United States county-level populations​

The same epydemix-data v1.2.0 update introduces ~3,100 US county-level populations (e.g. United_States__Massachusetts__Suffolk_County). Demographic distributions come from the US Census Bureau (2023); contact matrices are inherited from the corresponding state in the absence of county-specific survey data. See the Population Presets page for examples.

Documentation​

  • New Calculated parameters section in the Parameters guide: expression syntax, broadcasting/composition with transforms, reserved names, and an R0-calibration example
  • Note in the Parameter Transforms guide that target_parameter must be a source parameter (scalar or age-varying), not a calculated one
  • The Populations Overview R0-calibration section now points at CONTACT_MATRIX_EIGENVALUE_ALL as the in-request shortcut
  • The Population Presets page reflects the new double-underscore convention across all subnational identifiers, and adds a section on US county-level populations (~3,100 counties) with examples