C++11 random weibull_distribution


The The C++11 random weibull_distribution produces random numbers x ≥ 0 using the respective discrete probability function of the weibull_distribution-the function is shown at the end of the post.
The class declaration of the distribution is shown below.

template
class weibull_distribution ;

The distribution produces only floating point values and the default type of the distribution is double type.

The class types and all the member functions is given below.

Types

typedef RealType result_type;
typedef unspecified param_type;

The RealType is a type definition of the distribution type.And the param_type is a structure,however the definition will vary from compiler to compiler.

Constructors and reset function

explicit weibull_distribution(RealType a = 1.0, RealType b = 1.0);
explicit weibull_distribution(const param_type& parm);
void reset( );

The first constructor accept two parameters ‘a’ and ‘b’,they are used in calculating the probability of the random values in the distribution.The relation 0 < a and 0 < b.

The second constructor accept a reference to param_type object.If this constructor is called the ‘a’ and ‘b’ values is assigned from the ‘a’ and ‘b’ values of the param_type object-param_type constructor also accept two parameters ‘a’ and ‘b’.

Code example

weibull_distribution< > wd( 560 , 405);

weibull_distribution<float >::param_type pt( 88 , 99 );

weibull_distribution<float > wd1( pt) ; //’a’ is 88 and b is ’99’ which are assigned from the ‘a’ and ‘b’ of the pt object

weibull_distribution< > wd2( pt ) ; //error! , type of pt is float but type of wd2 is double type


 



Generating functions

template<class URNG>
result_type operator( )(URNG& g);
template<class URNG>
result_type operator( )(URNG& g, const param_type& parm);

the first operator() function

The generated random sequence is obtained using the operator() function.The first overloaded operator() accept URNG(Uniform Random Number Generator) or engine.

Code example

weibull_distribution< > wd( 560 , 405);

ranlux24_base r24 ;

cout<< wd(r24) << ” ” << wd(r24) ;

Output in Code::blocks,

404.759   405.467

the second operator( ) function

The second overloaded operator( ) function accept URNG and param_type object.

Code example

weibull_distribution<float >::param_type pt( 88 , 99 );

weibull_distribution<float > wd ;

default_random_engine dre ;

cout<< wd(dre , pt) << ” ” << wd(dre , pt) ;

Output in Code::blocks,

98.4522   96.8207


Property functions

result_type a( ) const ;
result_type b() const;
param_type param() const;
void param(const param_type& parm);
result_type min() const;
result_type max() const;

a() function

The a() function returns the value of ‘a’ parameter.

Code example

weibull_distribution< > wd( 560 , 405);

cout<< wd.a();

Output,

560

b() function

The b() function returns the value of ‘b’ parameter.

Code example

weibull_distribution< > wd( 560 , 405);

cout<< wd.b();

Output,

405

param( )

This function returns the param_type object.

Code example

weibull_distribution<float >::param_type pt( 88 , 99 );

cout<< pt.a() << endl; //param_type has it’s own version of a() function

weibull_distribution<float > wd(1000 , 200) ;

pt=wd.param( );

cout<< wd.a( ) << endl ;

Output,

88
1000

param(param_type)

Using this function we can change the ‘a’ and ‘b’ value of the distribution to the ‘a’ and ‘b’ value of the param_type object by passing the param_type object.

Code example

weibull_distribution<long double > wd ;

cout<< wd.param( ).b( ) << endl ; //same as wd.b( )

weibull_distribution<float >::param_type pt(34 , 90);

wd.param( pt );

cout<< wd.param().b() << endl ;

Output,

1
90

min() function

The min() returns the smallest value the distribution can generate,which is the value 0.

Code example

weibull_distribution< > wd(900 , 10) ;

cout<< wd.min( ) ;

Output,

0

max() function

The max() returns the smallest value the distribution can generate,which is the value 0.

Code example

weibull_distribution<long double > wd(900 , 10) ;

cout<< wd.max( ) ;

Output,

1.18973e+4932


*Side Note

weibull_distribution roduces random numbers x≥0 distributed according to the probability density function

weibull_distribution probability function.PNG


 


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