---

name: structured-expressions description: "Use when PySR needs TemplateExpressionSpec, parametric templates, shared or vector-valued expressions, differential operators, or seeded template guesses." disable-model-invocation: true metadata: disco-role: operating license: Apache 2.0

Structured expressions

Use this sub-skill when the equation shape is partly known and PySR should search only the unknown pieces.

Use this sub-skill for

• TemplateExpressionSpec planning or repair
• parametric expressions with category-specific learned constants
• shared subexpressions or vector-valued residual templates
• differential templates that use D
• seeded guesses for known template placeholders

Route to another sub-skill when

• the task is a free-form fit without known structure → fit-and-diagnose
• the task needs custom losses, operator constraints, or tree walks → customization-and-constraints
• the task needs SymPy / LaTeX / JAX / PyTorch exports or reload handling → export-and-artifacts

Operating rules

1. Keep the template shape explicit: combine, expressions, variable_names, and optional parameters.
2. Treat category indices as Julia indices inside the template. If the source labels are 0-based, shift them before fit.
3. For vector-valued templates, move the extra targets into X, use a dummy y, and make the elementwise loss return the residual from the template.
4. For differential templates, use D and verify the argument index.
5. Do not promise template export methods that are unsupported. Use model.equations_["julia_expression"] and component trees instead.
6. If the template also needs a custom objective, hand off to customization-and-constraints and use loss_function_expression.

Bundled assets

• references/template-workflows.md
• references/api-reference.md
• references/troubleshooting.md
• scripts/template_spec_builder.py

Verification target

A later agent should be able to build a valid template plan, explain indexing and parameters, seed guesses correctly, and identify unsupported exports without running a search.