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 *
 *  Copyright NumFOCUS
 *
 *  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
 *
 *         https://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 itkOnePlusOneEvolutionaryOptimizer_h
#define itkOnePlusOneEvolutionaryOptimizer_h

#include "itkSingleValuedNonLinearOptimizer.h"
#include "itkRandomVariateGeneratorBase.h"
#include "ITKOptimizersExport.h"
#include <string>

namespace itk
{
/** \class OnePlusOneEvolutionaryOptimizer
 * \brief 1+1 evolutionary strategy optimizer
 *
 * This optimizer searches for the optimal parameters. It changes its search
 * radius and position using the grow factor ,shrink factor, and isotropic
 * probability function (which is a random unit normal variate generator).
 *
 * This optimizer needs a cost function and a random unit normal
 * variate generator.
 * The cost function should return cost with new position in parameter space
 * which will be generated by 1+1 evolutionary strategy.
 * Users should plug-in the random unit normal variate generator using
 * SetNormalVariateGenerator method.
 *
 * The SetEpsilon method is the minimum value for the frobenius_norm of
 * the covariance matrix. If the fnorm is smaller than this value,
 * the optimization process will stop even before it hits the maximum
 * iteration.
 *
 * Another way to stop the optimization process is calling the
 * StopOptimization method. At next iteration after calling it, the
 * optimization process will stop.
 *
 * This optimizing scheme was initially developed and implemented
 * by Martin Styner, Univ. of North Carolina at Chapel Hill, and his
 * colleagues.
 *
 * For more details. refer to the following articles.
 * "Parametric estimate of intensity inhomogeneities applied to MRI"
 * Martin Styner, G. Gerig, Christian Brechbuehler, Gabor Szekely,
 * IEEE TRANSACTIONS ON MEDICAL IMAGING; 19(3), pp. 153-165, 2000,
 * (https://www.cs.unc.edu/~styner/docs/tmi00.pdf)
 *
 * "Evaluation of 2D/3D bias correction with 1+1ES-optimization"
 * Martin Styner, Prof. Dr. G. Gerig (IKT, BIWI, ETH Zuerich), TR-197
 * (https://www.cs.unc.edu/~styner/docs/StynerTR97.pdf)
 *
 * \ingroup Numerics Optimizers
 *
 * \sa NormalVariateGenerator
 * \ingroup ITKOptimizers
 */

class ITKOptimizers_EXPORT OnePlusOneEvolutionaryOptimizer : public SingleValuedNonLinearOptimizer
{
public:
  /** Standard "Self" type alias. */
  using Self = OnePlusOneEvolutionaryOptimizer;
  using Superclass = SingleValuedNonLinearOptimizer;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  /** Method for creation through the object factory. */
  itkNewMacro(Self);

  /** \see LightObject::GetNameOfClass() */
  itkOverrideGetNameOfClassMacro(OnePlusOneEvolutionaryOptimizer);

  /** Type of the Cost Function   */
  using CostFunctionType = SingleValuedCostFunction;
  using CostFunctionPointer = CostFunctionType::Pointer;

  /** Normal random variate generator type. */
  using NormalVariateGeneratorType = Statistics::RandomVariateGeneratorBase;

  /** Set if the Optimizer should Maximize the metric */
  itkSetMacro(Maximize, bool);
  itkBooleanMacro(Maximize);
  itkGetConstReferenceMacro(Maximize, bool);

  bool
  GetMinimize() const
  {
    return !m_Maximize;
  }
  void
  SetMinimize(bool v)
  {
    this->SetMaximize(!v);
  }
  void
  MinimizeOn()
  {
    SetMaximize(false);
  }
  void
  MinimizeOff()
  {
    SetMaximize(true);
  }

  /** Set/Get maximum iteration limit. */
  itkSetMacro(MaximumIteration, unsigned int);
  itkGetConstReferenceMacro(MaximumIteration, unsigned int);

  /** Set/Get the search radius grow factor in parameter space. */
  itkSetMacro(GrowthFactor, double);
  itkGetConstReferenceMacro(GrowthFactor, double);

  /** Set/Get the search radius shrink factor. */
  itkSetMacro(ShrinkFactor, double);
  itkGetConstReferenceMacro(ShrinkFactor, double);

  /** Set/Get initial search radius in parameter space */
  itkSetMacro(InitialRadius, double);
  itkGetConstReferenceMacro(InitialRadius, double);

  /** Set/Get the minimal size of search radius
   * (frobenius_norm of covariance matrix). */
  itkSetMacro(Epsilon, double);
  itkGetConstReferenceMacro(Epsilon, double);

  /** Get the current Frobenius norm of covariance matrix */
  itkGetConstReferenceMacro(FrobeniusNorm, double);

  void
  SetNormalVariateGenerator(NormalVariateGeneratorType * generator);

  /** Initializes the optimizer.
   * Before running this optimizer, this function should have been called.
   *
   * initialRadius: search radius in parameter space
   * grow: search radius grow factor
   * shrink: search radius shrink factor */
  void
  Initialize(double initialRadius, double grow = -1, double shrink = -1);

  /** Return Current Value */
  itkGetConstReferenceMacro(CurrentCost, MeasureType);
  MeasureType
  GetValue() const
  {
    return this->GetCurrentCost();
  }

  /** Return Current Iteration */
  itkGetConstReferenceMacro(CurrentIteration, unsigned int);

  /** Return if optimizer has been initialized */
  itkGetConstReferenceMacro(Initialized, bool);

  /** Start optimization.
   * Optimization will stop when it meets either of two termination conditions,
   * the maximum iteration limit or epsilon (minimal search radius)  */
  void
  StartOptimization() override;

  /** when users call StartOptimization, this value will be set false.
   * By calling StopOptimization, this flag will be set true, and
   * optimization will stop at the next iteration. */
  void
  StopOptimization()
  {
    m_Stop = true;
  }

  itkGetConstReferenceMacro(CatchGetValueException, bool);
  itkSetMacro(CatchGetValueException, bool);

  itkGetConstReferenceMacro(MetricWorstPossibleValue, double);
  itkSetMacro(MetricWorstPossibleValue, double);

  const std::string
  GetStopConditionDescription() const override;

protected:
  OnePlusOneEvolutionaryOptimizer();
  OnePlusOneEvolutionaryOptimizer(const OnePlusOneEvolutionaryOptimizer &);
  ~OnePlusOneEvolutionaryOptimizer() override = default;
  void
  PrintSelf(std::ostream & os, Indent indent) const override;

private:
  /** Smart pointer to the normal random variate generator. */
  NormalVariateGeneratorType::Pointer m_RandomGenerator{};

  /** Maximum iteration limit. */
  unsigned int m_MaximumIteration{};

  /** Current iteration */
  unsigned int m_CurrentIteration{};

  bool   m_CatchGetValueException{};
  double m_MetricWorstPossibleValue{};

  /** Set if the Metric should be maximized: Default = False */
  bool m_Maximize{};

  /** The minimal size of search radius
   * (frobenius_norm of covariance matrix). */
  double m_Epsilon{};

  /** Initial search radius in parameter space. */
  double m_InitialRadius{};

  /** Search radius growth factor in parameter space. */
  double m_GrowthFactor{};

  /** Search radius shrink factor in parameter space, */
  double m_ShrinkFactor{};

  /** Flag tells if the optimizer was initialized using Initialize function. */
  bool m_Initialized{};

  /** Internal storage for the value type / used as a cache  */
  MeasureType m_CurrentCost{};

  /** This is user-settable flag to stop optimization.
   * when users call StartOptimization, this value will be set false.
   * By calling StopOptimization, this flag will be set true, and
   * optimization will stop at the next iteration. */
  bool m_Stop{};

  /** Stop description */
  std::ostringstream m_StopConditionDescription{};

  /** Cache variable for reporting the Frobenius Norm
   */
  double m_FrobeniusNorm{};
}; // end of class
} // end of namespace itk

#endif