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/*=========================================================================
*
* Copyright UMC Utrecht and contributors
*
* 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.txt
*
* 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.
*
*=========================================================================*/
#include "itkStandardStochasticVarianceReducedGradientDescentOptimizer.h"
#include <vnl/vnl_math.h>
namespace itk
{
/**
* ************************* Constructor ************************
*/
StandardStochasticVarianceReducedGradientOptimizer::StandardStochasticVarianceReducedGradientOptimizer() = default;
/**
* ********************** StartOptimization *********************
*/
void
StandardStochasticVarianceReducedGradientOptimizer::StartOptimization()
{
this->m_CurrentTime = this->m_InitialTime;
this->Superclass::StartOptimization();
} // end StartOptimization
/**
* ******************** AdvanceOneStep **************************
*/
void
StandardStochasticVarianceReducedGradientOptimizer::AdvanceOneStep()
{
this->SetLearningRate(this->Compute_a(this->m_CurrentTime));
this->Superclass::AdvanceOneStep();
this->UpdateCurrentTime();
} // end AdvanceOneStep
/**
* ************************** Compute_a *************************
*/
double
StandardStochasticVarianceReducedGradientOptimizer::Compute_a(double k) const
{
return static_cast<double>(this->m_Param_a / std::pow(this->m_Param_A + k + 1.0, this->m_Param_alpha));
} // end Compute_a
/**
* ************************** Compute_beta *************************
*/
double
StandardStochasticVarianceReducedGradientOptimizer::Compute_beta(double k) const
{
return static_cast<double>(this->m_Param_beta / std::pow(this->m_Param_A + k + 1.0, this->m_Param_alpha));
} // end Compute_beta
/**
* ************************** UpdateCurrentTime ********************
*/
void
StandardStochasticVarianceReducedGradientOptimizer::UpdateCurrentTime()
{
/** Simply Robbins-Monro: time=iterationnr. */
this->m_CurrentTime += 1.0;
} // end UpdateCurrentTime
} // end namespace itk
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