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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 itkBSplineSecondOrderDerivativeKernelFunction2_h
#define itkBSplineSecondOrderDerivativeKernelFunction2_h
#include "itkKernelFunctionBase.h"
#include <vnl/vnl_math.h>
#include <cmath> // For abs.
namespace itk
{
/** \class BSplineSecondOrderDerivativeKernelFunction2
* \brief Derivative of a B-spline kernel used for density estimation and
* nonparametric regression.
*
* This class encapsulates the derivative of a B-spline kernel for
* density estimation or nonparametric regression.
* See documentation for KernelFunction for more details.
*
* This class is templated over the spline order.
* \warning Evaluate is only implemented for spline order 1 to 4
*
* \sa KernelFunction
*
* \ingroup Functions
*/
template <unsigned int VSplineOrder = 3>
class ITK_TEMPLATE_EXPORT BSplineSecondOrderDerivativeKernelFunction2 : public KernelFunctionBase<double>
{
public:
ITK_DISALLOW_COPY_AND_MOVE(BSplineSecondOrderDerivativeKernelFunction2);
/** Standard class typedefs. */
using Self = BSplineSecondOrderDerivativeKernelFunction2;
using Superclass = KernelFunctionBase<double>;
using Pointer = SmartPointer<Self>;
/** Method for creation through the object factory. */
itkNewMacro(Self);
/** Run-time type information (and related methods). */
itkTypeMacro(BSplineSecondOrderDerivativeKernelFunction2, KernelFunctionBase);
/** Enum of for spline order. */
itkStaticConstMacro(SplineOrder, unsigned int, VSplineOrder);
/** Evaluate the function. Faster than the corresponding public `Evaluate` member function, because it is
* static (whereas this `Evaluate` member function is virtual). */
static double
FastEvaluate(const double u)
{
return Self::Evaluate(Dispatch<VSplineOrder>(), u);
}
/** Evaluate the function. Faster than the corresponding public `Evaluate` member function, because it is
* static, so it does not require the creation of a `BSplineSecondOrderDerivativeKernelFunction2` object. */
static void
FastEvaluate(const double u, double * const weights)
{
Self::Evaluate(Dispatch<VSplineOrder>(), u, weights);
}
/** Evaluate the function. */
double
Evaluate(const double & u) const override
{
return Self::FastEvaluate(u);
}
/** Evaluate the function. */
void
Evaluate(const double u, double * weights) const
{
Self::FastEvaluate(u, weights);
}
protected:
BSplineSecondOrderDerivativeKernelFunction2() = default;
~BSplineSecondOrderDerivativeKernelFunction2() override = default;
void
PrintSelf(std::ostream & os, Indent indent) const override
{
Superclass::PrintSelf(os, indent);
os << indent << "Spline Order: " << SplineOrder << std::endl;
}
private:
/** Structures to control overloaded versions of Evaluate */
struct DispatchBase
{};
template <unsigned int>
struct ITK_TEMPLATE_EXPORT Dispatch : DispatchBase
{};
/** Zeroth order spline. */
// Second order derivative not defined.
/** First order spline */
// Second order derivative not defined.
/** Second order spline. */
static double
Evaluate(const Dispatch<2> &, const double u)
{
double absValue = std::abs(u);
if (absValue < 0.5)
{
return -2.0;
}
else if (absValue == 0.5)
{
return -0.5;
}
else if (absValue < 1.5)
{
return 1.0;
}
else if (absValue == 1.5)
{
return 0.5;
}
else
{
return 0.0;
}
}
static void
Evaluate(const Dispatch<2> &, const double, double * weights)
{
weights[0] = 1.0;
weights[1] = -2.0;
weights[2] = 1.0;
}
/** Third order spline. */
static double
Evaluate(const Dispatch<3> &, const double u)
{
const double absValue = std::abs(u);
if (absValue < 1.0)
{
return vnl_math::sgn0(u) * (3.0 * u) - 2.0;
}
else if (absValue < 2.0)
{
return -vnl_math::sgn(u) * u + 2.0;
}
else
{
return 0.0;
}
}
static void
Evaluate(const Dispatch<3> &, const double u, double * weights)
{
weights[0] = -u + 2.0;
weights[1] = 3.0 * u - 5.0;
weights[2] = -3.0 * u + 4.0;
weights[3] = u - 1.0;
}
/** Unimplemented spline order */
static double
Evaluate(const DispatchBase &, const double)
{
itkGenericExceptionMacro("Evaluate not implemented for spline order " << SplineOrder);
}
static void
Evaluate(const DispatchBase &, const double, double *)
{
itkGenericExceptionMacro("Evaluate not implemented for spline order " << SplineOrder);
}
};
} // end namespace itk
#endif
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