normal_distribution< drake::symbolic::Expression > Class Reference

Detailed Description

Provides std::normal_distribution, N(μ, σ), for symbolic expressions.

When operator() is called, it returns a symbolic expression μ + σ * v where v is a symbolic random variable associated with the standard normal (Gaussian) distribution.

It keeps a shared pointer to the vector of symbolic random variables that has been created for the following purposes:

• When reset() is called, it rewinds index_ to zero so that the next operator (re)-uses the first symbolic random variable.

  random_device rd;
  RandomGenerator g{rd()};
  std::normal_distribution<Expression> d(0.0, 1.0);
   
  const Expression e1{d(g)};
  const Expression e2{d(g)};
  d.reset();
  const Expression e3{d(g)};
   
  EXPECT_FALSE(e1.EqualTo(e2));
  EXPECT_TRUE(e1.EqualTo(e3));

• When an instance of this class is copied, the original and copied distributions share the vector of symbolic random variables. We want to make sure that the two generate identical sequences of elements.

  random_device rd;
  RandomGenerator g{rd()};
   
  std::normal_distribution<Expression> d1(0.0, 1.0);
  std::normal_distribution<Expression> d2(d1);
  const Expression e1_1{d1(g)};
  const Expression e1_2{d1(g)};
   
  const Expression e2_1{d2(g)};
  const Expression e2_2{d2(g)};
   
  EXPECT_TRUE(e1_1.EqualTo(e2_1));
  EXPECT_TRUE(e1_2.EqualTo(e2_2));

#include <drake/common/symbolic/expression/expression.h>

Public Types
using	RealType = drake::symbolic::Expression
using	result_type = RealType

Public Member Functions
	normal_distribution (RealType mean, RealType stddev=1.0)
	Constructs a new distribution object with mean and stddev.
	normal_distribution ()
	Constructs a new distribution object with mean = 0.0 and stddev = 1.0.
void	reset ()
	Resets the internal state of the distribution object.
result_type	operator() ()
	Generates a symbolic expression representing a random value that is distributed according to the associated probability function.
template<class Generator>
result_type	operator() (Generator &)
	Generates a symbolic expression representing a random value that is distributed according to the associated probability function.
RealType	mean () const
	Returns the mean μ distribution parameter.
RealType	stddev () const
	Returns the deviation σ distribution parameter.
result_type	min () const
	Returns the minimum potentially generated value.
result_type	max () const
	Returns the maximum potentially generated value.o.
Implements CopyConstructible, CopyAssignable, MoveConstructible, MoveAssignable
	normal_distribution (const normal_distribution &)=default
normal_distribution &	operator= (const normal_distribution &)=default
	normal_distribution (normal_distribution &&)=default
normal_distribution &	operator= (normal_distribution &&)=default

Friends
bool	operator== (const normal_distribution< drake::symbolic::Expression > &lhs, const normal_distribution< drake::symbolic::Expression > &rhs)

Member Typedef Documentation

RealType

using RealType = drake::symbolic::Expression

result_type

using result_type = RealType

Constructor & Destructor Documentation

normal_distribution() [1/4]

normal_distribution ( RealType mean, RealType stddev = 1.0 )

explicit

Constructs a new distribution object with mean and stddev.

Exceptions

std::exception

if stddev is a non-positive constant expression.

normal_distribution() [2/4]

normal_distribution

(

)

Constructs a new distribution object with mean = 0.0 and stddev = 1.0.

normal_distribution() [3/4]

normal_distribution ( const normal_distribution< drake::symbolic::Expression > & )

default

normal_distribution() [4/4]

normal_distribution ( normal_distribution< drake::symbolic::Expression > && )

default

Member Function Documentation

max()

result_type max ( ) const

nodiscard

Returns the maximum potentially generated value.o.

mean()

RealType mean ( ) const

nodiscard

Returns the mean μ distribution parameter.

min()

result_type min ( ) const

nodiscard

Returns the minimum potentially generated value.

Note

In libstdc++ std::normal_distribution<> defines min() and max() to return -DBL_MAX and DBL_MAX while the one in libc++ returns -INFINITY and INFINITY. We follows libc++ and return -INFINITY and INFINITY.

operator()() [1/2]

result_type operator()

(

)

Generates a symbolic expression representing a random value that is distributed according to the associated probability function.

operator()() [2/2]

template<class Generator>

result_type operator()

(

Generator &

)

Generates a symbolic expression representing a random value that is distributed according to the associated probability function.

Note

We provide this method, which takes a random generator, for compatibility with the std::normal_distribution::operator().

operator=() [1/2]

normal_distribution & operator= ( const normal_distribution< drake::symbolic::Expression > & )

default

operator=() [2/2]

normal_distribution & operator= ( normal_distribution< drake::symbolic::Expression > && )

default

reset()

void reset

(

)

Resets the internal state of the distribution object.

stddev()

RealType stddev ( ) const

nodiscard

Returns the deviation σ distribution parameter.

Friends And Related Symbol Documentation

operator==

bool operator== ( const normal_distribution< drake::symbolic::Expression > & lhs, const normal_distribution< drake::symbolic::Expression > & rhs )

friend

---

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

• drake/common/symbolic/expression/expression.h