C++11 weibull distribution random

The The C++11 weibull distribution ( or 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.

Link :C++11 random number generator
 

The class declaration of the distribution is shown below.

template<class RealType = double>
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.

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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.

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Constructors and reset function

explicit weibull_distribution(RealType a = 1.0, RealType b = 1.0);

explicit weibull_distribution(const param_type& parm);

void reset( ); 
[/coce]
<p>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 <b>0 &lt; a</b> and <b>0 &lt; b</b>.</p>

<p>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'.</p>

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

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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.

weibull_distribution< > wd( 560 , 405);

ranlux24_base r24 ;

cout<< wd(r24) << ” ” << wd(r24) ;

Output in Code::blocks,

the second operator( ) function

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

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,

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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.

weibull_distribution< > wd( 560 , 405);

cout<< wd.a(); 

Output,

b() function

The b() function returns the value of 'b' parameter.

weibull_distribution< > wd( 560 , 405);

cout<< wd.b();

Output,

param( )

This function returns the param_type object.

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,

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.

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,

min() function

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

weibull_distribution< > wd(900 , 10) ;

cout<< wd.min( ) ;

Output,

max() function

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

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

cout<< wd.max( ) ; 

Output,

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