The gamma distribution Random Number Generator (RNG) that allows stream numbers to be set deterministically. More...

#include "random-variable-stream.h"

Inheritance diagram for ns3::GammaRandomVariable:

Collaboration diagram for ns3::GammaRandomVariable:

Public Member Functions
	GammaRandomVariable ()
	Creates a gamma distribution RNG with the default values for alpha and beta.

double	GetAlpha () const
	Returns the alpha value for the gamma distribution returned by this RNG stream.

double	GetBeta () const
	Returns the beta value for the gamma distribution returned by this RNG stream.

virtual uint32_t	GetInteger ()
	Get the next random value drawn from the distribution.

uint32_t	GetInteger (uint32_t alpha, uint32_t beta)
	Get the next random value drawn from the distribution.

double	GetValue () override
	Get the next random value drawn from the distribution.

double	GetValue (double alpha, double beta)
	Get the next random value drawn from the distribution.

Public Member Functions inherited from ns3::RandomVariableStream
	RandomVariableStream ()
	Default constructor.

	RandomVariableStream (const RandomVariableStream &)=delete

	~RandomVariableStream () override
	Destructor.

int64_t	GetStream () const
	Returns the stream number for the RngStream.

bool	IsAntithetic () const
	Check if antithetic values will be generated.

RandomVariableStream &	operator= (const RandomVariableStream &)=delete

void	SetAntithetic (bool isAntithetic)
	Specify whether antithetic values should be generated.

void	SetStream (int64_t stream)
	Specifies the stream number for the RngStream.

Public Member Functions inherited from ns3::Object
	Object ()
	Constructor.

	~Object () override
	Destructor.

void	AggregateObject (Ptr< Object > other)
	Aggregate two Objects together.

void	Dispose ()
	Dispose of this Object.

AggregateIterator	GetAggregateIterator () const
	Get an iterator to the Objects aggregated to this one.

TypeId	GetInstanceTypeId () const override
	Get the most derived TypeId for this Object.

template<typename T >
Ptr< T >	GetObject () const
	Get a pointer to the requested aggregated Object.

template<>
Ptr< Object >	GetObject () const
	Specialization of () for objects of type ns3::Object.

template<typename T >
Ptr< T >	GetObject (TypeId tid) const
	Get a pointer to the requested aggregated Object by TypeId.

template<>
Ptr< Object >	GetObject (TypeId tid) const
	Specialization of (TypeId tid) for objects of type ns3::Object.

void	Initialize ()
	Invoke DoInitialize on all Objects aggregated to this one.

bool	IsInitialized () const
	Check if the object has been initialized.

void	UnidirectionalAggregateObject (Ptr< Object > other)
	Aggregate an Object to another Object.

Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
	SimpleRefCount ()
	Default constructor.

	SimpleRefCount (const SimpleRefCount &o)
	Copy constructor.

uint32_t	GetReferenceCount () const
	Get the reference count of the object.

SimpleRefCount &	operator= (const SimpleRefCount &o)
	Assignment operator.

void	Ref () const
	Increment the reference count.

void	Unref () const
	Decrement the reference count.

Public Member Functions inherited from ns3::ObjectBase
virtual	~ObjectBase ()
	Virtual destructor.

void	GetAttribute (std::string name, AttributeValue &value, bool permissive=false) const
	Get the value of an attribute, raising fatal errors if unsuccessful.

bool	GetAttributeFailSafe (std::string name, AttributeValue &value) const
	Get the value of an attribute without raising errors.

void	SetAttribute (std::string name, const AttributeValue &value)
	Set a single attribute, raising fatal errors if unsuccessful.

bool	SetAttributeFailSafe (std::string name, const AttributeValue &value)
	Set a single attribute without raising errors.

bool	TraceConnect (std::string name, std::string context, const CallbackBase &cb)
	Connect a TraceSource to a Callback with a context.

bool	TraceConnectWithoutContext (std::string name, const CallbackBase &cb)
	Connect a TraceSource to a Callback without a context.

bool	TraceDisconnect (std::string name, std::string context, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected with a context.

bool	TraceDisconnectWithoutContext (std::string name, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected without a context.

Static Public Member Functions
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::RandomVariableStream
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::Object
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::ObjectBase
static TypeId	GetTypeId ()
	Get the type ID.

Private Member Functions
double	GetNormalValue (double mean, double variance, double bound)
	Returns a random double from a normal distribution with the specified mean, variance, and bound.

Private Attributes
double	m_alpha
	The alpha value for the gamma distribution returned by this RNG stream.

double	m_beta
	The beta value for the gamma distribution returned by this RNG stream.

bool	m_nextValid
	True if the next normal value is valid.

double	m_v2
	The algorithm produces two values at a time.

double	m_y
	The algorithm produces two values at a time.

Additional Inherited Members
Protected Member Functions inherited from ns3::RandomVariableStream
RngStream *	Peek () const
	Get the pointer to the underlying RngStream.

Protected Member Functions inherited from ns3::Object
	Object (const Object &o)
	Copy an Object.

virtual void	DoDispose ()
	Destructor implementation.

virtual void	DoInitialize ()
	Initialize() implementation.

virtual void	NotifyNewAggregate ()
	Notify all Objects aggregated to this one of a new Object being aggregated.

Protected Member Functions inherited from ns3::ObjectBase
void	ConstructSelf (const AttributeConstructionList &attributes)
	Complete construction of ObjectBase; invoked by derived classes.

virtual void	NotifyConstructionCompleted ()
	Notifier called once the ObjectBase is fully constructed.

Related Symbols inherited from ns3::ObjectBase
static TypeId	GetObjectIid ()
	Ensure the TypeId for ObjectBase gets fully configured to anchor the inheritance tree properly.

Detailed Description

The gamma distribution Random Number Generator (RNG) that allows stream numbers to be set deterministically.

This class supports the creation of objects that return random numbers from a fixed gamma distribution. It also supports the generation of single random numbers from various gamma distributions.

The probability distribution is defined in terms two parameters, Alpha = $\alpha > 0$ and Beta = $\beta > 0$ . (Note the Wikipedia entry for the Gamma Distribution uses either the parameters $k, \theta$ or $\alpha, \beta$ . The parameters used here $(\alpha, \beta)_{\mbox{ns-3}}$ correspond to $(\alpha, \frac{1}{\beta})_{\mbox{Wikipedia}}$ .)

The probability density function is:

$P(x; \alpha, \beta) dx = x^{\alpha-1} \\ \frac{e^{-\frac{x}{\beta}}}{\beta^\alpha \Gamma(\alpha)} dx, \\ \quad x \in [0, +\infty)$

where the mean is $\mu = \alpha\beta$ and the variance is $\sigma^2 = \alpha \beta^2$ .

While gamma RNG values can be generated by an algorithm similar to normal RNGs, the implementation used here is based on the paper G. Marsaglia and W. W. Tsang, A simple method for generating Gamma variables, ACM Transactions on Mathematical Software, Vol. 26, No. 3, Sept. 2000.

Example

Here is an example of how to use this class:

double alpha = 5.0;
double beta = 2.0;
 
Ptr<GammaRandomVariable> x = CreateObject<GammaRandomVariable> ();
x->SetAttribute ("Alpha", DoubleValue (alpha));
x->SetAttribute ("Beta", DoubleValue (beta));
 
double value = x->GetValue ();

Antithetic Values.

If an instance of this RNG is configured to return antithetic values, the actual value returned, , is generated using the prescription in the Marsaglia, et al. paper cited above.

Definition at line 1247 of file random-variable-stream.h.

Constructor & Destructor Documentation

◆ GammaRandomVariable()

ns3::GammaRandomVariable::GammaRandomVariable ( )

Creates a gamma distribution RNG with the default values for alpha and beta.

Definition at line 927 of file random-variable-stream.cc.

References NS_LOG_FUNCTION.

Member Function Documentation

◆ GetAlpha()

double ns3::GammaRandomVariable::GetAlpha ( ) const

Returns the alpha value for the gamma distribution returned by this RNG stream.

Returns: The alpha value for the gamma distribution returned by this RNG stream.

Definition at line 936 of file random-variable-stream.cc.

References m_alpha.

◆ GetBeta()

double ns3::GammaRandomVariable::GetBeta ( ) const

Returns the beta value for the gamma distribution returned by this RNG stream.

Returns: The beta value for the gamma distribution returned by this RNG stream.

Definition at line 942 of file random-variable-stream.cc.

References m_beta.

◆ GetInteger() [1/2]

uint32_t ns3::RandomVariableStream::GetInteger ( )

virtual

Get the next random value drawn from the distribution.

Returns: A random value.

Reimplemented from ns3::RandomVariableStream.

Definition at line 144 of file random-variable-stream.cc.

◆ GetInteger() [2/2]

uint32_t ns3::GammaRandomVariable::GetInteger	(	uint32_t	alpha,
		uint32_t	beta )

Get the next random value drawn from the distribution.

Returns: A random value.

Parameters

[in]	alpha	Alpha value for the gamma distribution.
[in]	beta	Beta value for the gamma distribution.

◆ GetNormalValue()

double ns3::GammaRandomVariable::GetNormalValue	(	double	mean,
		double	variance,
		double	bound )

private

Returns a random double from a normal distribution with the specified mean, variance, and bound.

Parameters

[in]	mean	Mean value for the normal distribution.
[in]	variance	Variance value for the normal distribution.
[in]	bound	Bound on values returned.

Returns: A floating point random value.

Definition at line 1028 of file random-variable-stream.cc.

References ns3::RandomVariableStream::GetStream(), ns3::RandomVariableStream::IsAntithetic(), m_nextValid, m_v2, m_y, NS_LOG_DEBUG, ns3::RandomVariableStream::Peek(), and ns3::RngStream::RandU01().

Referenced by GetValue().

Here is the call graph for this function:

Here is the caller graph for this function:

◆ GetTypeId()

TypeId ns3::GammaRandomVariable::GetTypeId ( )

static

Register this type.

Returns: The object TypeId.

Definition at line 907 of file random-variable-stream.cc.

References m_alpha, m_beta, ns3::MakeDoubleAccessor(), ns3::MakeDoubleChecker(), and ns3::TypeId::SetParent().

Here is the call graph for this function:

◆ GetValue() [1/2]

double ns3::GammaRandomVariable::GetValue ( )

overridevirtual

Get the next random value drawn from the distribution.

Returns: A random value.

Implements ns3::RandomVariableStream.

Definition at line 1022 of file random-variable-stream.cc.

References GetValue(), m_alpha, and m_beta.

Referenced by GetValue(), and GetValue().

Here is the call graph for this function:

Here is the caller graph for this function:

◆ GetValue() [2/2]

double ns3::GammaRandomVariable::GetValue	(	double	alpha,
		double	beta )

Get the next random value drawn from the distribution.

Returns: A random value.

Parameters

[in]	alpha	Alpha value for the gamma distribution.
[in]	beta	Beta value for the gamma distribution.

Definition at line 964 of file random-variable-stream.cc.

References GetNormalValue(), ns3::RandomVariableStream::GetStream(), GetValue(), ns3::NormalRandomVariable::INFINITE_VALUE, ns3::RandomVariableStream::IsAntithetic(), NS_LOG_DEBUG, ns3::RandomVariableStream::Peek(), and ns3::RngStream::RandU01().

Here is the call graph for this function:

Member Data Documentation

◆ m_alpha

double ns3::GammaRandomVariable::m_alpha

private

The alpha value for the gamma distribution returned by this RNG stream.

Definition at line 1300 of file random-variable-stream.h.

Referenced by GetAlpha(), GetTypeId(), and GetValue().

◆ m_beta

double ns3::GammaRandomVariable::m_beta

private

The beta value for the gamma distribution returned by this RNG stream.

Definition at line 1303 of file random-variable-stream.h.

Referenced by GetBeta(), GetTypeId(), and GetValue().

◆ m_nextValid

bool ns3::GammaRandomVariable::m_nextValid

private

True if the next normal value is valid.

Definition at line 1306 of file random-variable-stream.h.

Referenced by GetNormalValue().

◆ m_v2

double ns3::GammaRandomVariable::m_v2

private

The algorithm produces two values at a time.

Cache parameters for possible reuse.

Definition at line 1309 of file random-variable-stream.h.

Referenced by GetNormalValue().

◆ m_y

double ns3::GammaRandomVariable::m_y

private

The algorithm produces two values at a time.

Cache parameters for possible reuse.

Definition at line 1311 of file random-variable-stream.h.

Referenced by GetNormalValue().

The documentation for this class was generated from the following files:

src/core/model/random-variable-stream.h
src/core/model/random-variable-stream.cc

Public Member Functions

Static Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ GammaRandomVariable()

Member Function Documentation

◆ GetAlpha()

◆ GetBeta()

◆ GetInteger() [1/2]

◆ GetInteger() [2/2]

◆ GetNormalValue()

◆ GetTypeId()

◆ GetValue() [1/2]

◆ GetValue() [2/2]

Member Data Documentation

◆ m_alpha

◆ m_beta

◆ m_nextValid

◆ m_v2

◆ m_y