charged-shells/charged_shells/patch_size.py

import numpy as np
from scipy.optimize import bisect, root_scalar
from charged_shells import expansion, mapping, parameters, potentials
from typing import Callable

Expansion = expansion.Expansion
Array = np.ndarray
ModelParams = parameters.ModelParams


@mapping.map_over_expansion
def charge_patch_size(ex: Expansion, phi: float = 0, theta0: Array | float = 0, theta1: Array | float = np.pi / 2):
    return bisect(lambda theta: ex.charge_value(theta, phi), theta0, theta1)


def potential_patch_size(ex: Expansion, params: ModelParams,
                         phi: float = 0, theta0: Array | float = 0, theta1: Array | float = np.pi / 2,
                         match_expansion_axis_to_params: int = None):

    # this is more complicate to map over leading axes of the expansion as potential also depends on model parameters,
    # with some, such as kappaR, also being the parameters of the expansion in the first place. When mapping,
    # we must therefore provide the expansion axis that should match the collection of parameters in params.

    @mapping.map_over_expansion
    def potential_zero(exp: Expansion, prms: ModelParams):
        return bisect(lambda theta: potentials.charged_shell_potential(theta, phi, 1, exp, prms), theta0, theta1)

    return mapping.parameter_map_single_expansion(potential_zero, match_expansion_axis_to_params)(ex, params)


def inverse_potential_patch_size(target_patch_size: float,
                                 ex_generator: Callable[[float], Expansion],
                                 x0: float,
                                 params: ModelParams, **ps_kwargs):

    def patch_size_dif(x):
        ex = ex_generator(x)
        return potential_patch_size(ex, params, **ps_kwargs) - target_patch_size

    root_result = root_scalar(patch_size_dif, x0=x0)

    if not root_result.converged:
        raise ValueError('No convergence. Patches of desired size might not be achievable in the given model. '
                         'Conversely, a common mistake might be target patch size input in degrees.')

    return root_result.root