"""
Fit a unit-aware diameter
=========================

Parameters can carry Pint units. The model receives values with the original
units, so the physics code does not need to know how the optimizer stores its
internal scalar coordinates.

The fitted diameter is approximately 120 nanometers: doubling it reproduces
the 240 nm observation. This scalar example demonstrates unit handling, not
a scattering forward model.
"""
from PyMieSim import FitParameter, MeasuredData, fit_parameters, ureg

observation = MeasuredData(values=240 * ureg.nanometer)


def model(parameters):
    diameter = parameters["diameter"]
    return 2 * diameter


result = fit_parameters(
    model=model,
    observation=observation,
    parameters=[
        FitParameter(
            name="diameter",
            initial=150 * ureg.nanometer,
            bounds=(50 * ureg.nanometer, 300 * ureg.nanometer),
        )
    ],
)

print(result.parameters["diameter"])