Source code for pde.pdes.diffusion

A simple diffusion equation

.. codeauthor:: David Zwicker <> 

from typing import Callable

import numpy as np

from ..fields import ScalarField
from ..grids.boundaries.axes import BoundariesData
from import fill_in_docstring
from import jit, nb
from .base import PDEBase, expr_prod

[docs]class DiffusionPDE(PDEBase): r"""A simple diffusion equation The mathematical definition is .. math:: \partial_t c = D \nabla^2 c where :math:`c` is a scalar field that is distributed with diffusivity :math:`D`. """ explicit_time_dependence = False @fill_in_docstring def __init__( self, diffusivity: float = 1, noise: float = 0, bc: BoundariesData = "auto_periodic_neumann", ): """ Args: diffusivity (float): The diffusivity of the described species noise (float): Strength of the (additive) noise term bc: The boundary conditions applied to the field. {ARG_BOUNDARIES} """ super().__init__(noise=noise) self.diffusivity = diffusivity self.bc = bc @property def expression(self) -> str: """str: the expression of the right hand side of this PDE""" return expr_prod(self.diffusivity, "laplace(c)")
[docs] def evolution_rate( # type: ignore self, state: ScalarField, t: float = 0, ) -> ScalarField: """evaluate the right hand side of the PDE Args: state (:class:`~pde.fields.ScalarField`): The scalar field describing the concentration distribution t (float): The current time point Returns: :class:`~pde.fields.ScalarField`: Scalar field describing the evolution rate of the PDE """ assert isinstance(state, ScalarField), "`state` must be ScalarField" laplace = state.laplace(bc=self.bc, label="evolution rate", args={"t": t}) return self.diffusivity * laplace # type: ignore
def _make_pde_rhs_numba( # type: ignore self, state: ScalarField ) -> Callable[[np.ndarray, float], np.ndarray]: """create a compiled function evaluating the right hand side of the PDE Args: state (:class:`~pde.fields.ScalarField`): An example for the state defining the grid and data types Returns: A function with signature `(state_data, t)`, which can be called with an instance of :class:`~numpy.ndarray` of the state data and the time to obtained an instance of :class:`~numpy.ndarray` giving the evolution rate. """ arr_type = nb.typeof( signature = arr_type(arr_type, nb.double) diffusivity_value = self.diffusivity laplace = state.grid.make_operator("laplace", bc=self.bc) @jit(signature) def pde_rhs(state_data: np.ndarray, t: float): """compiled helper function evaluating right hand side""" return diffusivity_value * laplace(state_data, args={"t": t}) return pde_rhs # type: ignore