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Lorentz.py
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Lorentz.py
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#pylint: disable=no-init,invalid-name
'''
@author Mathieu Doucet, ORNL
@date Oct 13, 2014
Copyright © 2007-8 ISIS Rutherford Appleton Laboratory, NScD Oak Ridge National Laboratory & European Spallation Source
This file is part of Mantid.
Mantid 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.
Mantid 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 this program. If not, see <http://www.gnu.org/licenses/>.
File change history is stored at: <https://github.com/mantidproject/mantid>
Code Documentation is available at: <http://doxygen.mantidproject.org>
'''
from __future__ import (absolute_import, division, print_function)
import math
import numpy as np
from mantid.api import IFunction1D, FunctionFactory
class Lorentz(IFunction1D):
"""
Provide a Lorentz model for SANS
I(q) = scale / ( 1 + q^2 L^2 ) + background
"""
def category(self):
return "SANS"
def init(self):
# Active fitting parameters
self.declareParameter("Scale", 1.0, 'Scale')
self.declareParameter("Length", 50.0, 'Length')
self.declareParameter("Background", 0.0, 'Background')
def function1D(self, xvals):
"""
Evaluate the model
@param xvals: numpy array of q-values
"""
return self.getParameterValue("Scale") / (1.0 + np.power(xvals*self.getParameterValue('Length'), 2)) +\
self.getParameterValue('Background')
def functionDeriv1D(self, xvals, jacobian):
"""
Evaluate the first derivatives
@param xvals: numpy array of q-values
@param jacobian: Jacobian object
"""
i = 0
for x in xvals:
jacobian.set(i,0, 1.0 / (1.0 + np.power(x*self.getParameterValue('Length'), 2)))
denom = math.pow(1.0 + math.pow(x*self.getParameterValue('Length'), 2), -2)
jacobian.set(i,1, -2.0 * self.getParameterValue("Scale") * x * x * self.getParameterValue('Length') * denom)
jacobian.set(i,2, 1.0)
i += 1
# Required to have Mantid recognise the new function
FunctionFactory.subscribe(Lorentz)