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# 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) 2013-2018 Max-Planck-Society
#
# NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
# and financially supported by the Studienstiftung des deutschen Volkes.
from .scaling_operator import ScalingOperator
from .laplace_operator import LaplaceOperator
def SmoothnessOperator(domain, strength=1., logarithmic=True, space=None):
"""An operator measuring the smoothness on an irregular grid with respect
to some scale.
This operator applies the irregular LaplaceOperator and its adjoint to some
Field over a PowerSpace which corresponds to its smoothness and weights the
result with a scale parameter sigma. It is used in the smoothness prior
terms of the CriticalPowerEnergy. For this purpose we use free boundary
conditions in the LaplaceOperator, having no curvature at both ends. In
addition the first entry is ignored as well, corresponding to the overall
mean of the map. The mean is therefore not considered in the smoothness
prior.
Parameters
----------
strength: nonnegative float
Specifies the strength of the SmoothnessOperator
logarithmic : boolean
Whether smoothness is calculated on a logarithmic scale or linear scale
default : True
"""
if strength < 0:
raise ValueError("ERROR: strength must be nonnegative.")
if strength == 0.:
return ScalingOperator(0., domain)
laplace = LaplaceOperator(domain, logarithmic=logarithmic, space=space)
return (strength**2)*laplace.adjoint*laplace