# This program 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.
#
# This program 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 .
#
# Copyright(C) 2013-2017 Max-Planck-Society
#
# NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
# and financially supported by the Studienstiftung des deutschen Volkes.
from .energy import Energy
class QuadraticEnergy(Energy):
"""The Energy for a quadratic form.
The most important aspect of this energy is that its curvature must be
position-independent.
"""
def __init__(self, position, A, b, _grad=None):
super(QuadraticEnergy, self).__init__(position=position)
self._A = A
self._b = b
if _grad is not None:
self._grad = _grad
Ax = _grad + self._b
else:
Ax = self._A(self.position)
self._grad = Ax - self._b
self._value = 0.5*self.position.vdot(Ax) - b.vdot(self.position)
def at(self, position):
return QuadraticEnergy(position=position, A=self._A, b=self._b)
def at_with_grad(self, position, grad):
return QuadraticEnergy(position=position, A=self._A, b=self._b,
_grad=grad)
@property
def value(self):
return self._value
@property
def gradient(self):
return self._grad
@property
def curvature(self):
return self._A