math_spec.transforms

Rewriting a model into the one a decomposition solves.

A myopic pathway, a rolling horizon and a Benders subproblem share one move: a variable stops being a decision and becomes a number somebody else chose. The subproblem is the same model at a capacity someone picked; the myopic step is the same model with what earlier periods already built. Written by hand that is a second file to keep in step with the first, and the drift between them is a bug nothing catches.

It is not every half of a decomposition. A Benders master is not the model with the dispatch fixed — it is the model with the dispatch gone, which is a different move and not this one. Fixing every variable a constraint names leaves a row that decides nothing, and the language says so.

It reads like a rename and it is not, which is why it is here rather than four lines in every driver. A fixed variable's mask becomes a claim about its data, and its domain becomes a dtype — two decisions a driver would each make differently, and one of them silently:

• A variable masked by where: has rows that do not exist. As a parameter those rows have no value, so it is coverage: masked. The obvious rewrite leaves it total, which claims every coordinate has a number and is the wrong answer that binds cleanly.
• A binary or integer variable becomes an int parameter, never a float one: the values are whole and a consumer reading the declaration is entitled to know it.

Bounds are dropped, and that is the one thing lost. They constrained a decision this model no longer makes; whether the numbers supplied respect them is a question about data, which this package does not have.

fix(model, *names)

model with each variable in names turned into a parameter of the same name.

Every expression naming one goes on reading, because the name does not move — which is what makes the rewrite mechanical. A myopic step fixes what earlier periods built, which is many at once, so the whole set is named in one call and validated once at the end of it.

PARAMETER	DESCRIPTION
model	Whatever every other verb takes. TYPE: str | Path | dict[str, Any] | Spec
names	Variables the model declares. Naming none is the model itself. TYPE: str DEFAULT: ()

RETURNS	DESCRIPTION
Spec	The model as a :class:~math_spec.model.Spec, revalidated — so a fix
Spec	that made the model unsayable says so here rather than downstream.

RAISES	DESCRIPTION
KeyError	One of names is not a variable, named with the near miss.
LanguageError	The fixed model is not one the language accepts — a constraint every variable of which is now a number, a set over one of them, or a curve linking one.

Source code in src/math_spec/transforms.py

def fix(model: str | Path | dict[str, Any] | Spec, *names: str) -> Spec:
    """*model* with each variable in *names* turned into a parameter of the same name.

    Every expression naming one goes on reading, because the name does not
    move — which is what makes the rewrite mechanical. A myopic step fixes
    what earlier periods built, which is many at once, so the whole set is
    named in one call and validated once at the end of it.

    Args:
        model: Whatever every other verb takes.
        names: Variables the model declares. Naming none is the model itself.

    Returns:
        The model as a :class:`~math_spec.model.Spec`, revalidated — so a fix
        that made the model unsayable says so here rather than downstream.

    Raises:
        KeyError: One of *names* is not a variable, named with the near miss.
        LanguageError: The fixed model is not one the language accepts — a
            constraint every variable of which is now a number, a set over one
            of them, or a curve linking one.
    """
    spec = to_spec(model).to_dict()
    variables = spec.get('variables') or {}
    for name in names:
        if name not in variables:
            raise KeyError(f"unknown variable '{name}'. " + did_you_mean(name, list(variables)))
        spec.setdefault('parameters', {})[name] = _as_parameter(variables.pop(name))
    return to_spec(spec)