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Public Member Functions | Static Public Member Functions | Private Attributes | List of all members
ns3::ExponentialRandomVariable Class Reference
Core » Random Variables

The exponential distribution Random Number Generator (RNG). More...

#include "random-variable-stream.h"

+ Inheritance diagram for ns3::ExponentialRandomVariable:
+ Collaboration diagram for ns3::ExponentialRandomVariable:

Public Member Functions

 ExponentialRandomVariable ()
 Creates an exponential distribution RNG with the default values for the mean and upper bound.
 
double GetBound () const
 Get the configured upper bound of this RNG.
 
virtual uint32_t GetInteger ()
 Get the next random value drawn from the distribution.
 
uint32_t GetInteger (uint32_t mean, uint32_t bound)
 Get the next random value drawn from the distribution.
 
double GetMean () const
 Get the configured mean value of this RNG.
 
double GetValue () override
 Get the next random value drawn from the distribution.
 
double GetValue (double mean, double bound)
 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_bound
 The upper bound on values that can be returned by this RNG stream.
 
double m_mean
 The mean value of the unbounded exponential distribution.
 

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
 Ensure the TypeId for ObjectBase gets fully configured to anchor the inheritance tree properly.
 

Detailed Description

The exponential distribution Random Number Generator (RNG).

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

The probability density function of an exponential variable is defined as:

\[ P(x; \alpha) dx = \alpha e^{-\alpha x} dx, \\ \quad x \in [0, +\infty) \]

where $ \alpha = \frac{1}{\mu} $ and $\mu$ is the Mean configurable attribute. This distribution has variance $ \sigma^2 = \alpha^2 $.

The exponential RNG value $x$ is generated by

\[ x = - \frac{\log(u)}{\alpha} = - \text{Mean} \log(u) \]

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

Bounded Distribution

Since the exponential distributions can theoretically return unbounded values, it is sometimes useful to specify a fixed upper Bound. The bounded version is defined over the interval $[0,b]$ as:

\[ P(x; \alpha, b) dx = \alpha e^{-\alpha x} dx, \\ \quad x \in [0, b] \]

Note that in this case the true mean of the distribution is smaller than the nominal mean value:

\[ \langle x | P(x; \alpha, b) \rangle = \frac{1}{\alpha} - \left(\frac{1}{\alpha} + b\right)\exp^{-\alpha b} \]

Example

Here is an example of how to use this class:

double mean = 3.14;
double bound = 0.0;
Ptr<ExponentialRandomVariable> x = CreateObject<ExponentialRandomVariable> ();
x->SetAttribute ("Mean", DoubleValue (mean));
x->SetAttribute ("Bound", DoubleValue (bound));
double value = x->GetValue ();
ns3::DoubleValue
This class can be used to hold variables of floating point type such as 'double' or 'float'.
Definition double.h:31
ns3::Ptr
Smart pointer class similar to boost::intrusive_ptr.
Definition mpi-test-fixtures.h:37
ns3::CreateObject
Ptr< T > CreateObject(Args &&... args)
Create an object by type, with varying number of constructor parameters.
Definition object.h:619
Antithetic Values.

If an instance of this RNG is configured to return antithetic values, the actual value returned, $x'$, is generated as follows:

\[ x' = - \frac{\log(1 - u)}{\alpha} = - Mean \log(1 - u), \]

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

Definition at line 542 of file random-variable-stream.h.

Constructor & Destructor Documentation

◆ ExponentialRandomVariable()

ns3::ExponentialRandomVariable::ExponentialRandomVariable ( )

Creates an exponential distribution RNG with the default values for the mean and upper bound.

Definition at line 387 of file random-variable-stream.cc.

References NS_LOG_FUNCTION.

Member Function Documentation

◆ GetBound()

double ns3::ExponentialRandomVariable::GetBound ( ) const

Get the configured upper bound of this RNG.

Returns
The upper bound.

Definition at line 400 of file random-variable-stream.cc.

References m_bound.

◆ 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::ExponentialRandomVariable::GetInteger ( uint32_t mean,
uint32_t bound )

Get the next random value drawn from the distribution.

Returns
A random value.
Parameters
[in]meanMean value of the unbounded exponential distribution.
[in]boundUpper bound on values returned.

Definition at line 431 of file random-variable-stream.cc.

References ns3::RandomVariableStream::GetStream(), GetValue(), NS_LOG_DEBUG, and NS_LOG_FUNCTION.

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◆ GetMean()

double ns3::ExponentialRandomVariable::GetMean ( ) const

Get the configured mean value of this RNG.

Note
This will not be the actual mean if the distribution is truncated by a bound.
Returns
The configured mean value.

Definition at line 394 of file random-variable-stream.cc.

References m_mean.

◆ GetTypeId()

TypeId ns3::ExponentialRandomVariable::GetTypeId ( )
static

Register this type.

Returns
The object TypeId.

Definition at line 367 of file random-variable-stream.cc.

References m_bound, m_mean, ns3::MakeDoubleAccessor(), ns3::MakeDoubleChecker(), and ns3::TypeId::SetParent().

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◆ GetValue() [1/2]

double ns3::ExponentialRandomVariable::GetValue ( )
overridevirtual

Get the next random value drawn from the distribution.

Returns
A random value.

Implements ns3::RandomVariableStream.

Definition at line 441 of file random-variable-stream.cc.

References GetValue(), m_bound, and m_mean.

Referenced by GetInteger(), and GetValue().

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◆ GetValue() [2/2]

double ns3::ExponentialRandomVariable::GetValue ( double mean,
double bound )

Get the next random value drawn from the distribution.

Returns
A random value.
Parameters
[in]meanMean value of the unbounded exponential distribution.
[in]boundUpper bound on values returned.

Definition at line 406 of file random-variable-stream.cc.

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

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Member Data Documentation

◆ m_bound

double ns3::ExponentialRandomVariable::m_bound
private

The upper bound on values that can be returned by this RNG stream.

Definition at line 591 of file random-variable-stream.h.

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

◆ m_mean

double ns3::ExponentialRandomVariable::m_mean
private

The mean value of the unbounded exponential distribution.

Definition at line 588 of file random-variable-stream.h.

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

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