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# coding: utf-8 |
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# Copyright (c) 2020 Stefan Bender |
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# |
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# This file is part of pyeppaurora. |
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# pyeppaurora is free software: you can redistribute it or modify |
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# it under the terms of the GNU General Public License as published |
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# by the Free Software Foundation, version 2. |
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# See accompanying LICENSE file or http://www.gnu.org/licenses/gpl-2.0.html. |
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"""Particle precipitation spectra |
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Includes variants describing a normalized particle flux, |
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as well as variants describing a normalized energy flux. |
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""" |
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import numpy as np |
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__all__ = [ |
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"exp_general", |
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"gaussian_general", |
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"maxwell_general", |
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"pow_general", |
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"pflux_exp", |
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"pflux_gaussian", |
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"pflux_maxwell", |
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"pflux_pow", |
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] |
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# General normalized spectra, standard distributions |
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def exp_general(en, en_0=10.): |
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r"""Exponential number flux spectrum as in Aksnes et al., 2006 [0] |
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Defined according to Aksnes et al., JGR 2006, Eq. (1), |
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normalized to unit number flux, i.e. |
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:math:`\int_0^\infty \phi(E) \text{d}E = 1`. |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV] of the distribution. |
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Default: 10 keV |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Normalized differential hemispherical number flux at `en` in [keV-1 cm-2 s-1] |
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([keV] or scaled by 1 keV-2 cm-2 s-1, e.g. ). |
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""" |
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return 1. / en_0 * np.exp(-en / en_0) |
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def gaussian_general(en, en_0=10., w=1.): |
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r"""Gaussian number flux spectrum as in Fang2008 [1] |
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Standard normal distribution with mu = en_0 and sigma = w / sqrt(2) |
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for use in Fang et al., JGR 2008, Eq. (1). |
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Almost normalized to unit number flux, i.e. |
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:math:`\int_0^\infty \phi(E) \text{d}E = 1` |
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(ignoring the negative tail). |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV |
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w: float, optional |
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Width of the Gaussian distribution, in [keV]. |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Normalized differential hemispherical number flux at `en` in [keV-1 cm-2 s-1] |
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([keV] or scaled by 1 keV-2 cm-2 s-1, e.g.). |
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""" |
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return 1. / np.sqrt(np.pi * w**2) * np.exp(-(en - en_0)**2 / w**2) |
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def maxwell_general(en, en_0=10.): |
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r"""Maxwell number flux spectrum as in Fang2008 [1] |
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Defined in Fang et al., JGR 2008, Eq. (1), |
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normalized to :math:`\int_0^\infty \phi(E) \text{d}E = 1`. |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Normalized differential hemispherical number flux at `en` in [keV-1 cm-2 s-1] |
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([keV] or scaled by 1 keV-2 cm-2 s-1, e.g.). |
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""" |
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return en / en_0**2 * np.exp(-en / en_0) |
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View Code Duplication |
def pow_general(en, en_0=10., gamma=-3., het=True): |
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r"""Power-law number flux spectrum as in Strickland1993 [3] |
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Defined e.g. in Strickland et al., 1993, |
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normalized to unit particle flux: |
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:math:`\int_{E_0}^\infty \phi(E) \text{d}E = 1` |
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for the high-energy tail version, and |
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:math:`\int_0^{E_0} \phi(E) \text{d}E = 1` |
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for the low-energy tail version. |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV |
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gamma: float, optional |
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Exponent of the power-law distribution, in [keV]. |
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het: bool, optional |
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Return a high-energy tail (het, default: true) for en > en_0, |
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or low-energy tail (false) for en < en_0. |
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Adjusts the normalization accordingly. |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Normalized differential hemispherical number flux at `en` in [keV-1 cm-2 s-1] |
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([keV] or scaled by 1 keV-2 cm-2 s-1, e.g.). |
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""" |
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spec = (gamma + 1) / en_0 * (en / en_0)**gamma |
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if het: |
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spec[en < en_0] = 0. |
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return -spec |
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spec[en > en_0] = 0. |
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return spec |
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def pflux_exp(en, en_0=10.): |
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r"""Exponential particle flux spectrum |
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Normalized to unit energy flux: |
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:math:`\int_0^\infty \phi(E) E \text{d}E = 1`. |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV. |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Hemispherical differential particle flux at `en` in [keV-1 cm-2 s-1] |
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([kev-2] scaled by unit energy flux). |
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""" |
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return exp_general(en, en_0=en_0) / en_0 |
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def pflux_gaussian(en, en_0=10., w=1): |
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r"""Gaussian particle flux spectrum |
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Defined in Fang et al., JGR 2008, Eq. (1). |
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Normalized to :math:`\int_0^\infty \phi(E) E \text{d}E = 1`. |
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(ignoring the negative tail). |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV. |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Hemispherical differential particle flux at `en` in [keV-1 cm-2 s-1] |
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([kev-2] scaled by unit energy flux). |
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""" |
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return gaussian_general(en, en_0=en_0, w=w) / en_0 |
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def pflux_maxwell(en, en_0=10.): |
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r"""Maxwell particle flux spectrum as in Fang2008 [1] |
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Defined in Fang et al., JGR 2008, Eq. (1). |
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The total precipitating energy flux is fixed to 1 keV cm-2 s-1, |
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multiply by Q_0 [keV cm-2 s-1] to scale the particle flux. |
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Normalized to :math:`\int_0^\infty \phi(E) E \text{d}E = 1`. |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV. |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Hemispherical differential particle flux at `en` in [keV-1 cm-2 s-1] |
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([kev-2] scaled by unit energy flux). |
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""" |
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return 0.5 / en_0 * maxwell_general(en, en_0) |
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def pflux_pow(en, en_0=10., gamma=-3., het=True): |
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r"""Power-law particle flux spectrum |
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Defined e.g. in Strickland et al., 1993. |
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Normalized to :math:`\int_{E_0}^\infty \phi(E) E \text{d}E = 1` |
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for the high-energy tail version, and to |
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:math:`\int_0^{E_0} \phi(E) E \text{d}E = 1` |
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for the low-energy tail version. |
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Parameters |
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---------- |
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en: float or array_like (N,) |
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Energy in [keV] |
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en_0: float, optional |
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Characteristic energy in [keV], i.e. mode of the distribution. |
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Default: 10 keV |
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gamma: float, optional |
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Exponent of the power-law distribution, in [keV]. |
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het: bool, optional (default True) |
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Return a high-energy tail (true) for en > en_0, |
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or low-energy tail (false) for en < en_0. |
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Adjusts the normalization accordingly. |
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Returns |
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------- |
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phi: float or array_like (N,) |
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Hemispherical differential particle flux at `en` in [keV-1 cm-2 s-1] |
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([kev-2] scaled by unit energy flux). |
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""" |
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return (gamma + 2) / (gamma + 1) / en_0 * pow_general(en, en_0=en_0, gamma=gamma, het=het) |
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