E-CE0601 — Invalid key in a fixed-variables dictionary

Error Type	Compile Error
Phase	configuring fixed_variables for evaluation
Python exception	TypeError (builtin)

Message

Invalid key of type `{type_name}` in the dictionary fixing an indexed variable in `fixed_variables`.

Each key must be one of the following:
  - an integer
  - a string
  - a tuple of integers and strings

Possible fix: use the variable's subscripts as the key (e.g. `(0, 1)` or `"label"`).

({type_name} is the Python type of the offending key)

Cause

An entry in the fixed_variables argument (of Problem.eval, Problem.generate_random_instance, or the Compiler constructor) fixes an indexed decision variable with a dictionary mapping subscripts to values, and one of the keys was neither an integer, a string, nor a tuple. For example, fixed_variables={"x": {0.5: 1.0}} raises this error because 0.5 is not a valid subscript. Keys identify which element of the variable to fix: for a variable with a single index the key can be a plain integer or string, and for multiple indices it must be a tuple of integers and strings.

Fix

Use the variable’s subscripts as the dictionary keys:

problem.eval(
    instance_data,
    fixed_variables={
        "x": {0: 1.0, 1: 0.0},   # one subscript per element
        "y": {(0, "a"): 2.0},    # multiple subscripts as a tuple
    },
)

Make sure the subscripts are plain Python int or str values (or tuples of them), matching how the variable is indexed in the model.

Related

E-CE0600 — the value side of the same dictionary is not numeric. E-CE0602 — the whole entry for a variable is neither a number nor a dictionary. E-TE0610 — raised instead when the key is a tuple but one of its elements is not an integer or string.