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# -*- coding: utf-8 -*-
# CCP in Tomographic Imaging (CCPi) Core Imaging Library (CIL).
# Copyright 2017 UKRI-STFC
# Copyright 2017 University of Manchester
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from ccpi.optimisation.functions import Function
import numpy
import warnings
# Define a class for squared 2-norm
class Norm2Sq(Function):
'''
f(x) = c*||A*x-b||_2^2
which has
grad[f](x) = 2*c*A^T*(A*x-b)
and Lipschitz constant
L = 2*c*||A||_2^2 = 2*s1(A)^2
where s1(A) is the largest singular value of A.
'''
def __init__(self, A, b, c=1.0):
super(Norm2Sq, self).__init__()
self.A = A # Should be an operator, default identity
self.b = b # Default zero DataSet?
self.c = c # Default 1.
self.range_tmp = A.range_geometry().allocate()
# Compute the Lipschitz parameter from the operator if possible
# Leave it initialised to None otherwise
try:
self.L = 2.0*self.c*(self.A.norm()**2)
except AttributeError as ae:
pass
except NotImplementedError as noe:
pass
#def grad(self,x):
# return self.gradient(x, out=None)
def __call__(self, x):
#return self.c* np.sum(np.square((self.A.direct(x) - self.b).ravel()))
#if out is None:
# return self.c*( ( (self.A.direct(x)-self.b)**2).sum() )
#else:
y = self.A.direct(x)
y.__isub__(self.b)
#y.__imul__(y)
#return y.sum() * self.c
try:
return y.squared_norm() * self.c
except AttributeError as ae:
# added for compatibility with SIRF
return (y.norm()**2) * self.c
def gradient(self, x, out=None):
if out is not None:
#return 2.0*self.c*self.A.adjoint( self.A.direct(x) - self.b )
self.A.direct(x, out=self.range_tmp)
self.range_tmp -= self.b
self.A.adjoint(self.range_tmp, out=out)
#self.direct_placehold.multiply(2.0*self.c, out=out)
out *= (self.c * 2.0)
else:
return (2.0*self.c)*self.A.adjoint(self.A.direct(x) - self.b)
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