def create_initial_assignments_model(species):
    """Create initial assignments for the model. Here only the formal type
    is defined. Assigning values to the parameters is done by
    :func:`create_parameters_model`.

    Parameters
    ----------
    species : list of strings
        List containing the names of all species.

    Returns
    -------
    assignments: dict
        Dictionary that contains the assignment names as keys
        and dicitonaries that contain the species' ids, and formulas
        as values.
    """

    all_species = species.keys()
    assignments = {}
    for index_species in all_species:
        keys = f"assignment_{index_species}"
        assignments[keys] = {
            "species_id": index_species,
            "formula": f"{index_species}_t0",
        }
    return assignments