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

#include "random-variable-stream.h"

Inheritance diagram for ns3::ZipfRandomVariable:

Collaboration diagram for ns3::ZipfRandomVariable:

Public Member Functions
	ZipfRandomVariable ()
	Creates a Zipf distribution RNG with the default values for n and alpha.

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

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

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

uint32_t	GetN () const
	Returns the n value for the Zipf distribution returned by this RNG stream.

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

double	GetValue (uint32_t n, double alpha)
	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 Attributes
double	m_alpha
	The alpha value for the Zipf distribution returned by this RNG stream.

double	m_c
	The normalization constant.

uint32_t	m_n
	The n value for the Zipf distribution returned by this RNG stream.

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 Zipf 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 Zipf distribution. It also supports the generation of single random numbers from various Zipf distributions.

Zipf's law states that given some corpus of natural language utterances, the frequency of any word is inversely proportional to its rank in the frequency table.

Zipf's distribution has two parameters, Alpha and N, where: $\alpha \ge 0$ (real) and $N \in \{1,2,3 \dots\}$ (integer). (Note the Wikipedia entry for the Zipf Distribution uses the symbol instead of $\alpha$ .)

The probability mass function is:

$P(k; \alpha, N) = \frac{1}{k^\alpha H_{N,\alpha}}$

where the N-th generalized harmonic number is

$H_{N,\alpha} = \sum_{m=1}^N \frac{1}{m^\alpha}$

Note the Zipf distribution is a discrete distribution, so the returned values will always be integers in the range $k \in {1,2 \dots N}$ .

The mean of the distribution is

$\mu = \frac{H_{N,\alpha - 1}}{H_{N,\alpha}}$

The Zipf RNG value is the smallest value such that

$u < \frac{H_k,\alpha}{H_N,\alpha}$

where is a uniform random variable on [0,1).

Example

Here is an example of how to use this class:

uint32_t n = 1;
double alpha = 2.0;
 
Ptr<ZipfRandomVariable> x = CreateObject<ZipfRandomVariable> ();
x->SetAttribute ("N", IntegerValue (n));
x->SetAttribute ("Alpha", DoubleValue (alpha));
 
double value = x->GetValue ();