text: /*=========================================================================
   *
   *  Copyright Insight Software Consortium
   *
   *  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 itkKernelFunctionBase_h
  #define itkKernelFunctionBase_h
  
  #include "itkFunctionBase.h"
  #include "itkConceptChecking.h"
  #include "itkNumericTraits.h"
  #include "itkMath.h"
  
  namespace itk
  {
  /** \class KernelFunctionBase
   * \brief Kernel used for density estimation and nonparameteric regression.
   *
   * This class encapsulates the smoothing kernel used for statistical density
   * estimation and nonparameteric regression. The basic idea of the kernel
   * approach is to weight observations by a smooth function (the kernel)
   * to created a smoothed approximation.
   *
   * Reference:
   * Silverman, B. W. (1986) Density Estimation. London: Chapman and Hall.
   *
   * \ingroup Functions
   * \ingroup ITKCommon
   */
  template <typename TRealValueType = double>
  class KernelFunctionBase : public FunctionBase<TRealValueType, TRealValueType>
  {
  public:
    /** Standard class type aliases. */
    using Self = KernelFunctionBase;
    using Superclass = FunctionBase<TRealValueType, TRealValueType>;
    using Pointer = SmartPointer<Self>;
    using ConstPointer = SmartPointer<const Self>;
  
    using RealType = TRealValueType;
  
    /** Run-time type information (and related methods). */
    itkTypeMacro(KernelFunctionBase, FunctionBase);
  
    /** Evaluate the function. Subclasses must implement this. */
    TRealValueType
    Evaluate(const TRealValueType & u) const override = 0;
  
  #ifdef ITK_USE_CONCEPT_CHECKING
    // Begin concept checking
    itkConceptMacro(TRealValueTypeIsFloatingPointCheck, (Concept::IsFloatingPoint<TRealValueType>));
    // End concept checking
  #endif
  
  protected:
    KernelFunctionBase() = default;
    ~KernelFunctionBase() override = default;
    void
    PrintSelf(std::ostream & os, Indent indent) const override
    {
      Superclass::PrintSelf(os, indent);
    }
  };
  } // end namespace itk
  
  #endif // itkKernelFunctionBase_h
  