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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.
*
*=========================================================================*/
#ifndef itkExponentialLimiterFunction_hxx
#define itkExponentialLimiterFunction_hxx
#include "itkExponentialLimiterFunction.h"
#include <vnl/vnl_math.h>
namespace itk
{
/**
* *************** Constructor ********************
*/
template <class TInput, unsigned int NDimension>
ExponentialLimiterFunction<TInput, NDimension>::ExponentialLimiterFunction()
{
this->ComputeLimiterSettings();
} // end Constructor
/**
* **************** Initialize ***********************
*/
template <class TInput, unsigned int NDimension>
void
ExponentialLimiterFunction<TInput, NDimension>::Initialize()
{
this->ComputeLimiterSettings();
} // end Initialize()
/**
* ******************** Evaluate ***********************
*/
template <class TInput, unsigned int NDimension>
auto
ExponentialLimiterFunction<TInput, NDimension>::Evaluate(const InputType & input) const -> OutputType
{
/** Apply a soft limit if the input is larger than the UpperThreshold */
const double diffU = static_cast<double>(input - this->m_UpperThreshold);
if (diffU > 1e-10)
{
return static_cast<OutputType>(this->m_UTminUB * std::exp(this->m_UTminUBinv * diffU) + this->m_UpperBound);
}
/** Apply a soft limit if the input is smaller than the LowerThreshold */
const double diffL = static_cast<double>(input - this->m_LowerThreshold);
if (diffL < -1e-10)
{
return static_cast<OutputType>(this->m_LTminLB * std::exp(this->m_LTminLBinv * diffL) + this->m_LowerBound);
}
/** Leave the value as it is */
return static_cast<OutputType>(input);
} // end Evaluate()
/**
* *********************** Evaluate *************************
*/
template <class TInput, unsigned int NDimension>
auto
ExponentialLimiterFunction<TInput, NDimension>::Evaluate(const InputType & input, DerivativeType & derivative) const
-> OutputType
{
/** Apply a soft limit if the input is larger than the UpperThreshold */
const double diffU = static_cast<double>(input - this->m_UpperThreshold);
if (diffU > 1e-10)
{
const double temp = this->m_UTminUB * std::exp(this->m_UTminUBinv * diffU);
const double gradientfactor = this->m_UTminUBinv * temp;
for (unsigned int i = 0; i < Dimension; ++i)
{
derivative[i] = static_cast<DerivativeValueType>(derivative[i] * gradientfactor);
}
return static_cast<OutputType>(temp + this->m_UpperBound);
}
/** Apply a soft limit if the input is smaller than the LowerThreshold */
const double diffL = static_cast<double>(input - this->m_LowerThreshold);
if (diffL < -1e-10)
{
const double temp = this->m_LTminLB * std::exp(this->m_LTminLBinv * diffL);
const double gradientfactor = this->m_LTminLBinv * temp;
for (unsigned int i = 0; i < Dimension; ++i)
{
derivative[i] = static_cast<DerivativeValueType>(derivative[i] * gradientfactor);
}
return static_cast<OutputType>(temp + this->m_LowerBound);
}
/** Leave the value and derivative as they are */
return static_cast<OutputType>(input);
} // end Evaluate()
/**
* ******************** ComputeLimiterSettings ********************
*/
template <class TInput, unsigned int NDimension>
void
ExponentialLimiterFunction<TInput, NDimension>::ComputeLimiterSettings()
{
this->m_UTminUB = static_cast<double>(this->m_UpperThreshold) - this->m_UpperBound;
this->m_LTminLB = static_cast<double>(this->m_LowerThreshold) - this->m_LowerBound;
if (this->m_UTminUB < -1e-10)
{
this->m_UTminUBinv = 1.0 / this->m_UTminUB;
}
else
{
/** The result is a hard limiter */
this->m_UTminUB = 0.0;
this->m_UTminUBinv = 0.0;
}
if (this->m_LTminLB > 1e-10)
{
this->m_LTminLBinv = 1.0 / this->m_LTminLB;
}
else
{
/** The result is a hard limiter */
this->m_LTminLB = 0.0;
this->m_LTminLBinv = 0.0;
}
} // end ComputeLimiterSettings()
} // end namespace itk
#endif
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