param (pmrf.param)

pmrf.param(*, default: Any = <dataclasses._MISSING_TYPE object>, as_free: bool = False, as_fixed: bool = False, constraint: AbstractConstraint | None = None, scale: float | None = None, **kwargs) → Any

A field specifier for registering parameters within a model.

This specifier can be used when declaring custom models inheriting from pmrf.Model.

It is used to register the parameter when a model is constructed, so it is listed by pmrf.params(). It can also be used to enforce constraints, scaling, bounds and variability within the model itself.

constraint is the parameter’s validity, such as a positive width: it always holds. A range the value brings, such as pmrf.Bounded(), is intersected with it, and a prior is truncated to the result and renormalised.

This simply creates a pmrf.field with a pmrf.as_param converter.

Example

Declaring a parameter with a positive constraint and built-in scale:

import pmrf as prf
from pmrf.parameters.constraints import Positive

class RC(prf.Module):
    R: prf.Param = prf.param(constraint=Positive())
    C: prf.Param = prf.param(constraint=Positive(), scale=1e-12)

rc = RC(1.0, 2.0)
rc.C.value            # 2.0, in pF
rc.C.physical_value   # 2e-12

RC(1.0, prf.Unconstrained(2.0, scale=1e-9)).C.physical_value
# 2e-09: an explicit scale overrides the field's

RC(-1.0, 2.0)
# ValueError: out of bounds
Parameters:

  • default (Any, optional) – The default value of the parameter.

  • constraint (Optional[AbstractConstraint], optional) – The constraint to apply to the parameter, in declared space. See pmrf.parameters.constraints.

  • scale (float, optional) – The units values of this field are written in, by default None (1.0). A parameter passed with its own scale keeps it.

  • as_free (bool, optional) – Whether to enforce that the value is a variable parameter. If False, incoming values will keep the variability (e.g. constants will remain constants). If True, all values will be co-erced into variable parameters.

  • as_fixed (bool, optional) – Whether to enforce that the value is a fixed parameter. If False, incoming values will keep the variability (e.g. constants will remain constants). If True, all values will be wrapped in pmrf.Fixed().

  • **kwargs – Additional key-word arguments to pass to the general pmrf.field() specifier.

Returns:

An equinox field with a built-in converter for parameter rules.

Return type:

Any