# NIFTy
# Copyright (C) 2017 Theo Steininger
#
# Author: Theo Steininger
#
# 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 .
from nifty import PowerSpace,\
Field,\
DiagonalOperator,\
FFTOperator
__all__ = ['create_power_operator']
def create_power_operator(domain, power_spectrum, dtype=None,
distribution_strategy='not'):
"""Creates a diagonal operator with a certain power spectrum.
Constructs a diagonal operator that lives over the specified domain, or
its harmonic domain in case it is not harmonic.
Parameters
----------
domain : DomainObject
Domain over which the power operator shall live. If this is not a
harmonic domain, it will return an operator for its harmonic domain
instead.
power_spectrum : {array-like, method}
An array-like object, or a method that implements the square root
of a power spectrum as a function of k.
dtype : type, *optional*
dtype that the field holding the power spectrum shall use
{default : None}
if dtype == None: passes this on to constructor of Field
distribution_strategy : string, *optional*
Distributed strategy to be used by the underlying d2o objects.
{default : 'not'}
Returns
-------
DiagonalOperator : An operator that lives that implements the given power
spectrum.
"""
if not domain.harmonic:
fft = FFTOperator(domain)
domain = fft.target[0]
power_domain = PowerSpace(domain,
distribution_strategy=distribution_strategy)
fp = Field(power_domain,
val=power_spectrum, dtype=dtype,
distribution_strategy=distribution_strategy)
fp **= 2
f = fp.power_synthesize(mean=1, std=0, real_signal=False)
power_operator = DiagonalOperator(domain, diagonal=f, bare=True)
return power_operator