# -*- coding: utf-8 -*-
################################ Begin license #################################
# Copyright (C) Laboratory of Imaging technologies,
# Faculty of Electrical Engineering,
# University of Ljubljana.
#
# This file is part of PyXOpto.
#
# PyXOpto is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# PyXOpto is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with PyXOpto. If not, see <https://www.gnu.org/licenses/>.
################################# End license ##################################
import numpy as np
from .pfbase import PfBase
[docs]class DoubleHg(PfBase):
def __init__(self, g1: float, g2: float, b: float):
'''
Double Henyey-Greenstein scattering phase function constructor.
Parameters
----------
g1: float
Anisotropy factor of the first Henyey-Greenstein scattering phase function.
g2: float
Anisotropy factor of the second Henyey-Greenstein scattering phase function.
b: float
Fractional contribution of the first Henyey-Greenstein phase function.
Examples
--------
Double Henyey-Greenstein scattering phase function for anisotropy
factors g = {0, 0.3 0.5, 0.8, 0.9, 0.95}.
>>> import numpy as np
>>> from matplotlib import pyplot as pp
>>>
>>> cos_theta = np.linspace(-1.0, 1.0, 1000)
>>>
>>> pp.figure()
>>> for g in [0, 0.3, 0.5, 0.8, 0.9, 0.95]:
>>> pf = DoubleHg(g, -g, 0.5)
>>> pp.semilogy(cos_theta, pf(cos_theta), label='g1={}, g2={}, b=0.5'.format(g, -g))
>>> pp.legend()
'''
super().__init__()
eps = np.finfo(np.float64).eps
self._g1 = max(min(g1, 1.0 - eps), -1 + eps)
self._g2 = max(min(g2, 1.0 - eps), -1 + eps)
self._b = min(max(float(b), 0.0), 1.0)
def __call__(self, costheta: float or np.ndarray) -> float or np.ndarray:
'''
Call method of the Double Henyey-Greenstein scattering phase function.
Parameters
----------
costheta: float or np.ndarray
Scattering angle cosines at which the scattering phase function
is evaluated.
Returns
-------
f: float or np.ndarray
Scattering phase function at the specified scattering angle cosines.
'''
return self._b*0.5*(1.0 - self._g1*self._g1)/ \
(1 + self._g1*self._g1 - 2*self._g1*costheta)**1.5 + \
(1.0 - self._b)*0.5*(1.0 - self._g2*self._g2)/ \
(1 + self._g2*self._g2 - 2*self._g2*costheta)**1.5
def __repr__(self):
return 'DoubleHg(g1={}, g2={}, b={})'.format(
self._g1, self._g2, self._b)