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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 itkMembershipFunctionBase_h
#define itkMembershipFunctionBase_h
#include "itkFunctionBase.h"
#include "itkMeasurementVectorTraits.h"
#include "itkNumericTraitsCovariantVectorPixel.h"
namespace itk
{
namespace Statistics
{
/**
* \class MembershipFunctionBase
* \brief MembershipFunctionBase defines common interfaces
* for membership functions.
*
* MembershipFunctionBase is a subclass of FunctionBase which
* restricts the function type to be a membership function. Membership
* functions provide a mapping from an arbitrary domain to a set of
* real numbers. Membership functions are typically used to model or
* approximate likelihood functions, \f$p( x | i )\f$, i.e. the
* probability of the measurement \f$x\f$ belonging to a class
* \f$i\f$.
*
* The Statistics framework models random variables \f$x\f$ as
* vectors. Typical uses of MembershipFunctions include templating
* over a FixedArray, Array, Vector, or VariableLengthVector.
*
* The Evaluate() method returns the membership rank or likelihood
* that the measurement belongs to the class represented by this
* membership function.
*
* Evaluations of a single measurement across of set MembershipFunctions
* can then be passed to a DecisionRule in order to establish
* class (or group) assignment.
*
* \ingroup ITKStatistics
*/
template <typename TVector>
class ITK_TEMPLATE_EXPORT MembershipFunctionBase : public FunctionBase<TVector, double>
{
public:
ITK_DISALLOW_COPY_AND_MOVE(MembershipFunctionBase);
/** Standard class type aliases */
using Self = MembershipFunctionBase;
using Superclass = FunctionBase<TVector, double>;
using Pointer = SmartPointer<Self>;
using ConstPointer = SmartPointer<const Self>;
/** \see LightObject::GetNameOfClass() */
itkOverrideGetNameOfClassMacro(MembershipFunctionBase);
/** MeasurementVector type alias support */
using MeasurementVectorType = TVector;
/** Typedef for the length of each measurement vector */
using MeasurementVectorSizeType = unsigned int;
/** Method to get membership score (discriminant score) of an entity
* or measurement. Evaluate() maps from a vector measurement type
* to a real number. */
double
Evaluate(const MeasurementVectorType & x) const override = 0;
/** Set the length of the measurement vector. If this membership
* function is templated over a vector type that can be resized,
* the new size is set. If the vector type has a fixed size and an
* attempt is made to change its size, an exception is
* thrown. Subclasses may have to override this method if a change
* in vector size requires invalidating other instance variables,
* e.g. covariance matrices, mean vectors, etc. */
virtual void
SetMeasurementVectorSize(MeasurementVectorSizeType s)
{
// Test whether the vector type is resizable or not
if (MeasurementVectorTraits::IsResizable<MeasurementVectorType>({}))
{
// then this is a resizable vector type
//
// if the new size is the same as the previous size, just return
if (s == this->m_MeasurementVectorSize)
{
return;
}
else
{
this->m_MeasurementVectorSize = s;
this->Modified();
}
}
else
{
// If this is a non-resizable vector type
MeasurementVectorSizeType defaultLength = NumericTraits<MeasurementVectorType>::GetLength({});
// and the new length is different from the default one, then throw an
// exception
if (defaultLength != s)
{
itkExceptionMacro("Attempting to change the measurement vector size of a non-resizable vector type");
}
}
}
/** Get the length of the measurement vector */
itkGetConstMacro(MeasurementVectorSize, MeasurementVectorSizeType);
protected:
MembershipFunctionBase()
{
m_MeasurementVectorSize = NumericTraits<MeasurementVectorType>::GetLength(MeasurementVectorType());
}
~MembershipFunctionBase() override = default;
void
PrintSelf(std::ostream & os, Indent indent) const override
{
Superclass::PrintSelf(os, indent);
os << indent << "Length of measurement vectors: " << m_MeasurementVectorSize << std::endl;
}
private:
MeasurementVectorSizeType m_MeasurementVectorSize{};
}; // end of class
} // end of namespace Statistics
} // end namespace itk
#endif
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