The Random Number Generator (RNG) that has a specified empirical distribution. More...

#include "random-variable-stream.h"

Inheritance diagram for ns3::EmpiricalRandomVariable:

Collaboration diagram for ns3::EmpiricalRandomVariable:

Classes
class	ValueCDF
	Helper to hold one point of the CDF. More...

Public Member Functions
	EmpiricalRandomVariable (void)
	Creates an empirical RNG that has a specified, empirical distribution, and configured for interpolating mode. More...

void	CDF (double v, double c)
	Specifies a point in the empirical distribution. More...

virtual uint32_t	GetInteger (void)
	Returns the next value in the empirical distribution. More...

virtual double	GetValue (void)
	Returns the next value in the empirical distribution. More...

virtual double	Interpolate (void)
	Returns the next value in the empirical distribution using linear interpolation. More...

bool	SetInterpolate (bool interpolate)
	Switch the mode between sampling the CDF and interpolating. More...

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

virtual	~RandomVariableStream ()
	Destructor. More...

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

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

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

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

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

virtual	~Object ()
	Destructor. More...

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

void	Dispose (void)
	Dispose of this Object. More...

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

virtual TypeId	GetInstanceTypeId (void) const
	Get the most derived TypeId for this Object. More...

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

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

template<>
Ptr< Object >	GetObject () const

template<>
Ptr< Object >	GetObject (TypeId tid) const

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

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

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

	SimpleRefCount (const SimpleRefCount &o)
	Copy constructor. More...

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

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

void	Ref (void) const
	Increment the reference count. More...

void	Unref (void) const
	Decrement the reference count. More...

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

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

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

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

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

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

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

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

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

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

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

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

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

Private Member Functions
double	DoInterpolate (double r)
	Linear interpolation between two points on the CDF to estimate the value at `r`. More...

double	DoSampleCDF (double r)
	Sample the CDF as a histogram (without interpolation). More...

bool	PreSample (double &value)
	Do the initial rng draw and check against the extrema. More...

void	Validate (void)
	Check that the CDF is valid. More...

Private Attributes
std::vector< ValueCDF >	m_emp
	The vector of CDF points. More...

bool	m_interpolate
	If `true` GetValue will interpolate, otherwise treat CDF as normal histogram. More...

bool	m_validated
	`true` once the CDF has been validated. More...

Friends
bool	operator< (ValueCDF a, ValueCDF b)
	Comparison operator, for use by std::upper_bound. More...

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

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

virtual void	DoDispose (void)
	Destructor implementation. More...

virtual void	DoInitialize (void)
	Initialize() implementation. More...

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

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

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

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

Detailed Description

The Random Number Generator (RNG) that has a specified empirical distribution.

Defines a random variable that has a specified, empirical distribution. The cumulative probability distribution function (CDF) is specified by a series of calls to the CDF() member function, specifying a value and the probability that the distribution is less than the specified value. When random values are requested, a uniform random variable r is used to select a probability, and the return value is chosen from the largest input value with CDF less than the random value. The method is known as inverse transform sampling: (http://en.wikipedia.org/wiki/Inverse_transform_sampling).

This generator has two modes: sampling and interpolating. In sampling mode this random variable generator treats the CDF as an exact histogram and returns one of the histogram inputs exactly. This is appropriate when the configured CDF represents the exact probability distribution, for a categorical variable, for example.

In interpolating mode this random variable generator linearly interpolates between the CDF values defining the histogram bins. This is appropriate when the configured CDF is an approximation to a continuous underlying probability distribution.

For historical reasons the default is interpolating. To switch modes use the Interpolate Attribute, or call SetInterpolate(). You can change modes at any time.

If you find yourself switching frequently it could be simpler to set the mode to sampling, then use the GetValue() function for sampled values, and Interpolate() function for interpolated values.

The CDF need not start with a probability of zero, nor end with a probability of 1.0. If the selected uniform random value r is less than the first CDF point, that point is selected. If r is greater than the last CDF point the last point is selected. In either case the interpolating mode will not interpolate (since there is no value beyond r to work with), but simply return the extremal CDF value, as in sampling.

Here is an example of how to use this class:

// Create the RNG with a non-uniform distribution between 0 and 10. // in sampling mode. Ptr<EmpiricalRandomVariable> x = CreateObject<EmpiricalRandomVariable> (); x->SetInterpolate (false); x->CDF ( 0.0, 0.0); x->CDF ( 5.0, 0.25); x->CDF (10.0, 1.0);

double value = x->GetValue ();

The expected values and probabilities returned by GetValue are

Value	Probability
0.0	0
5.0	25%
10.0	75%

The only two values ever returned are 5 and 10, with unequal probability.

If instead you want linear interpolation between the points of the CDF use the Interpolate() function:

double interp = x->Interpolate ();

This will return continuous values on the range [0,1).

See empirical-random-variable-example.cc for an example.

Config Paths

ns3::EmpiricalRandomVariable is accessible through the following paths with Config::Set and Config::Connect:

"/NodeList/[i]/DeviceList/[i]/$ns3::SimpleNetDevice/ReceiveErrorModel/$ns3::RateErrorModel/RanVar/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::SimpleNetDevice/ReceiveErrorModel/$ns3::BurstErrorModel/BurstStart/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::SimpleNetDevice/ReceiveErrorModel/$ns3::BurstErrorModel/BurstSize/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::PointToPointNetDevice/ReceiveErrorModel/$ns3::RateErrorModel/RanVar/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::PointToPointNetDevice/ReceiveErrorModel/$ns3::BurstErrorModel/BurstStart/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::PointToPointNetDevice/ReceiveErrorModel/$ns3::BurstErrorModel/BurstSize/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::CsmaNetDevice/ReceiveErrorModel/$ns3::RateErrorModel/RanVar/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::CsmaNetDevice/ReceiveErrorModel/$ns3::BurstErrorModel/BurstStart/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::CsmaNetDevice/ReceiveErrorModel/$ns3::BurstErrorModel/BurstSize/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::SixLowPanNetDevice/MeshUnderJitter/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::LrWpanNetDevice/Channel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Channel/$ns3::YansWifiChannel/PropagationDelayModel/$ns3::RandomPropagationDelayModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phy/PostReceptionErrorModel/$ns3::RateErrorModel/RanVar/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phy/PostReceptionErrorModel/$ns3::BurstErrorModel/BurstStart/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WifiNetDevice/Phy/PostReceptionErrorModel/$ns3::BurstErrorModel/BurstSize/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Channel/$ns3::SpectrumChannel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Channel/$ns3::YansWifiChannel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/Channel/$ns3::YansWifiChannel/PropagationDelayModel/$ns3::RandomPropagationDelayModel/Variable/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/PhyEntities/[i]/PostReceptionErrorModel/$ns3::RateErrorModel/RanVar/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/PhyEntities/[i]/PostReceptionErrorModel/$ns3::BurstErrorModel/BurstStart/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/DeviceList/[i]/$ns3::WaveNetDevice/PhyEntities/[i]/PostReceptionErrorModel/$ns3::BurstErrorModel/BurstSize/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/ApplicationList/[i]/$ns3::DhcpClient/Transactions/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/ApplicationList/[i]/$ns3::OnOffApplication/OnTime/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/ApplicationList/[i]/$ns3::OnOffApplication/OffTime/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::GaussMarkovMobilityModel/MeanVelocity/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::GaussMarkovMobilityModel/MeanDirection/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::GaussMarkovMobilityModel/MeanPitch/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomDirection2dMobilityModel/Speed/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomDirection2dMobilityModel/Pause/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWalk2dMobilityModel/Direction/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWalk2dMobilityModel/Speed/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/Speed/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/Pause/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomRectanglePositionAllocator/X/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomRectanglePositionAllocator/Y/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomBoxPositionAllocator/X/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomBoxPositionAllocator/Y/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomBoxPositionAllocator/Z/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomDiscPositionAllocator/Theta/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::RandomDiscPositionAllocator/Rho/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::OutdoorPositionAllocator/X/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::OutdoorPositionAllocator/Y/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWaypointMobilityModel/PositionAllocator/$ns3::OutdoorPositionAllocator/Z/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWalk2dOutdoorMobilityModel/Direction/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::MobilityModel/$ns3::RandomWalk2dOutdoorMobilityModel/Speed/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::ArpL3Protocol/RequestJitter/$ns3::EmpiricalRandomVariable"
"/NodeList/[i]/$ns3::Icmpv6L4Protocol/SolicitationJitter/$ns3::EmpiricalRandomVariable"
"/ChannelList/[i]/$ns3::SpectrumChannel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/ChannelList/[i]/$ns3::YansWifiChannel/PropagationLossModel/$ns3::RandomPropagationLossModel/Variable/$ns3::EmpiricalRandomVariable"
"/ChannelList/[i]/$ns3::YansWifiChannel/PropagationDelayModel/$ns3::RandomPropagationDelayModel/Variable/$ns3::EmpiricalRandomVariable"

Attributes

Interpolate: Treat the CDF as a smooth distribution and interpolate, default is to treat the CDF as a histogram and sample.
- Set with class: BooleanValue
- Underlying type: bool
- Initial value: false
- Flags: construct write read

Attributes defined in parent class ns3::RandomVariableStream

Stream: The stream number for this RNG stream. -1 means "allocate a stream automatically". Note that if -1 is set, Get will return -1 so that it is not possible to know which value was automatically allocated.
- Set with class: ns3::IntegerValue
- Underlying type: int64_t -9223372036854775808:9223372036854775807
- Initial value: -1
- Flags: construct write read
Antithetic: Set this RNG stream to generate antithetic values
- Set with class: BooleanValue
- Underlying type: bool
- Initial value: false
- Flags: construct write read

No TraceSources are defined for this type.
Size of this type is 96 bytes (on a 64-bit architecture).

Definition at line 2480 of file random-variable-stream.h.

Constructor & Destructor Documentation

◆ EmpiricalRandomVariable()

ns3::EmpiricalRandomVariable::EmpiricalRandomVariable ( void )

Creates an empirical RNG that has a specified, empirical distribution, and configured for interpolating mode.

Definition at line 1559 of file random-variable-stream.cc.

References NS_LOG_FUNCTION.

Member Function Documentation

◆ CDF()

void ns3::EmpiricalRandomVariable::CDF	(	double	v,
		double	c
	)

Specifies a point in the empirical distribution.

Note: These MUST be inserted in ascending order of c

Parameters

[in]	v	The function value for this point
[in]	c	Probability that the function is less than or equal to `v`

Definition at line 1692 of file random-variable-stream.cc.

References m_emp, and NS_LOG_FUNCTION.

Referenced by ns3::test::RandomVariable::EmpiricalTestCase::DoRun().

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◆ DoInterpolate()

double ns3::EmpiricalRandomVariable::DoInterpolate ( double r )

private

Linear interpolation between two points on the CDF to estimate the value at r.

Parameters

[in] r The argument value to interpolate to.

Returns: The interpolated CDF at r

Definition at line 1665 of file random-variable-stream.cc.

References m_emp, and NS_LOG_FUNCTION.

Referenced by GetValue(), and Interpolate().

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◆ DoSampleCDF()

double ns3::EmpiricalRandomVariable::DoSampleCDF ( double r )

private

Sample the CDF as a histogram (without interpolation).

Parameters

[in] r The CDF value at which to sample the CDF.

Returns: The bin value corresponding to r.

Definition at line 1638 of file random-variable-stream.cc.

References m_emp, and NS_LOG_FUNCTION.

Referenced by GetValue().

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◆ GetInteger()

uint32_t ns3::EmpiricalRandomVariable::GetInteger ( void )

virtual

Returns the next value in the empirical distribution.

Returns: The integer next value in the empirical distribution.

Note that this does not interpolate the CDF, but treats it as a stepwise continuous function. Also note that antithetic values are being generated if m_isAntithetic is equal to true. If $u$ is a uniform variable over [0,1] and $x$ is a value that would be returned normally, then $(1 - u$ ) is the distance that $u$ would be from $1$ . The value returned in the antithetic case, $x'$ , uses (1-u), which is the distance $u$ is from the 1.

Implements ns3::RandomVariableStream.

Definition at line 1575 of file random-variable-stream.cc.

References GetValue(), and NS_LOG_FUNCTION.

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◆ GetTypeId()

TypeId ns3::EmpiricalRandomVariable::GetTypeId ( void )

static

Register this type.

Returns: The object TypeId.

Definition at line 1544 of file random-variable-stream.cc.

References m_interpolate, ns3::MakeBooleanAccessor(), ns3::MakeBooleanChecker(), and ns3::TypeId::SetParent().

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◆ GetValue()

double ns3::EmpiricalRandomVariable::GetValue ( void )

virtual

Returns the next value in the empirical distribution.

Returns: The floating point next value in the empirical distribution.

Note that this does not interpolate the CDF, but treats it as a stepwise continuous function.

Also note that antithetic values are being generated if m_isAntithetic is equal to true. If $u$ is a uniform variable over [0,1] and $x$ is a value that would be returned normally, then $(1 - u$ ) is the distance that $u$ would be from $1$ . The value returned in the antithetic case, $x'$ , uses (1-u), which is the distance $u$ is from the 1.

Implements ns3::RandomVariableStream.

Definition at line 1615 of file random-variable-stream.cc.

References DoInterpolate(), DoSampleCDF(), m_interpolate, NS_LOG_FUNCTION, and PreSample().

Referenced by ns3::test::RandomVariable::EmpiricalTestCase::DoRun(), GetInteger(), RunBothModes(), and RunSingleSample().

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