#include <itkCacheableScalarFunction.h>

Detailed Description

function cache implementation

This is the base class for continuous scalar functions which needs cache for their pre-evaluated function returns.

The internal cache is created using the upper- and lower-bound domain values of the functional form (f(x))of subclasses of this class. So the cache only stores pre-evaluated values between f(lower-bound) and f(upper-bound).

To create a cache for continuous function, it uses sampling. With the given sample number , upper-bound, and lower-bound, it calculates interval within the ranges. It pre-evaluates and save f(x) where x = lower-bound + interval * [0 - sample number]

If a subclass of this class want to use a cache, it should explicitly call CreateCache(...) member function. GetCachedValue(x) will return pre-evaluated f(x) value. However, the return value from GetCachedValue(x) might be different from the exact return value from f(x) which is Evaluate(x) member function of subclasses of this class, because The GetCachedValue(x) member function internally converts x to cache table index and the conversion involves with truncation. So, users can think the cached value as an approximate to exact function return.

In some case, approximate values can be useful. For example, CompositeValleyFunction can be used as an M-estimator and it is currently used for MRIBiasFieldCorrectionFilter as an energy function. The bias field estimation requires calculation of energy values again and again for each iteration.

Definition at line 60 of file itkCacheableScalarFunction.h.

Inheritance diagram for itk::CacheableScalarFunction:

Collaboration diagram for itk::CacheableScalarFunction:

Public Types
using	MeasureArrayType = Array<MeasureType>

using	MeasureType = double

Public Member Functions
	CacheableScalarFunction ()

virtual MeasureType	Evaluate (MeasureType x)

MeasureType	GetCachedValue (MeasureType x)

double	GetCacheLowerBound () const

double	GetCacheUpperBound () const

double	GetInterval () const

SizeValueType	GetNumberOfSamples () const

bool	IsCacheAvailable () const

virtual	~CacheableScalarFunction ()

Protected Member Functions
void	CreateCache (double lowerBound, double upperBound, SizeValueType sampleSize)

Private Attributes
bool	m_CacheAvailable { false }

double	m_CacheLowerBound { 0.0 }

MeasureArrayType	m_CacheTable {}

double	m_CacheUpperBound { 0.0 }

SizeValueType	m_NumberOfSamples { 0 }

double	m_TableInc { 0.0 }

Member Typedef Documentation

◆ MeasureArrayType

using itk::CacheableScalarFunction::MeasureArrayType = Array<MeasureType>

Definition at line 71 of file itkCacheableScalarFunction.h.

◆ MeasureType

using itk::CacheableScalarFunction::MeasureType = double

Function's input and output value type.

Definition at line 70 of file itkCacheableScalarFunction.h.

Constructor & Destructor Documentation

◆ CacheableScalarFunction()

itk::CacheableScalarFunction::CacheableScalarFunction ( )

Constructor.

◆ ~CacheableScalarFunction()

virtual itk::CacheableScalarFunction::~CacheableScalarFunction ( )

virtual

Destructor.

Member Function Documentation

◆ CreateCache()

void itk::CacheableScalarFunction::CreateCache	(	double	lowerBound,
		double	upperBound,
		SizeValueType	sampleSize )

protected

Create the internal cache table and fill it with pre-evaluated values.

◆ Evaluate()

virtual MeasureType itk::CacheableScalarFunction::Evaluate ( MeasureType x )

virtual

y = f(x) Subclasses of this class should override this member function to provide their own functional operation .

Reimplemented in itk::CompositeValleyFunction.

◆ GetCachedValue()

MeasureType itk::CacheableScalarFunction::GetCachedValue ( MeasureType x )

inline

y = f(x) = (approximately) cache_table(index(x)) Get the function return using the internal cache table NOTE: Since the index calculation needs conversion from double to int, truncation happens. As a result, the return values from Evaluate(x) and GetCachedValue(x) may not be same for the same x.

Definition at line 121 of file itkCacheableScalarFunction.h.

References m_CacheLowerBound, m_CacheTable, m_CacheUpperBound, and m_TableInc.

Referenced by itk::CompositeValleyFunction::operator()().