gmx::TabulatedNormalDistribution< RealType, tableBits > Class Template Reference

#include <gromacs/random/tabulatednormaldistribution.h>

Description

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>
class gmx::TabulatedNormalDistribution< RealType, tableBits >

Tabulated normal random distribution.

Random distribution compatible with C++11 distributions - it can be used with any C++11 random engine.

Template Parameters

RealType	Type of the return value. Float or double. Note that GROMACS uses "real" type by default in contrast to the C++11 standard library, to avoid double/float conversions.
tableBits	Size of the table, specified in bits. The storage space required is sizeof(RealType)*2^tableBits. To keep things sane this is limited to 24 bits.

Some stochastic integrators depend on drawing a lot of normal distribution random numbers quickly, but in many cases the only important property is the distribution - given the noise in forces we do not need very high resolution. This distribution uses an internal table to return samples from a normal distribution with limited resolution. By default the table uses c_TabulatedNormalDistributionDefaultBits bits, but this is specified with a template parameter.

Since this distribution only uses tableBits bits per value generated, the values draw from the random engine are used for several results. To make sure you get a reproducible result when using counter-based random engines (such as ThreeFry2x64), remember to call the reset() method to cancel the internal memory of the distribution.

Note

For modern NUMA systems, you likely want to use separate distributions for each thread, and make sure they are initialized on the CPU where they will run, so the table is placed in that NUMA memory pool.

The finite table resolution means this distribution will NOT return arbitrarily small/large values, but with e.g. 14 bits the results are limited to roughly +/- 4 standard deviations.

Classes
class	param_type
	Normal distribution parameter class (mean and stddev) More...

Public Types
typedef RealType	result_type
	Type of normal distribution results.

Public Member Functions
	TabulatedNormalDistribution (result_type mean=0.0, result_type stddev=1.0)
	Construct new normal distribution with specified mean & stdddev. More...
	TabulatedNormalDistribution (const param_type &param)
	Construct new normal distribution from parameter type. More...
result_type	min () const
	Smallest value that can be generated in normal distributon. More...
result_type	max () const
	Largest value that can be generated in normal distribution. More...
result_type	mean () const
	Mean of the present normal distribution.
result_type	stddev () const
	Standard deviation of the present normal distribution.
param_type	param () const
	The parameter class (mean & stddev) of the normal distribution.
void	reset ()
	Clear all internal saved random bits from the random engine.
template<class Rng >
result_type	operator() (Rng &g)
	Return normal distribution value specified by internal parameters. More...
template<class Rng >
result_type	operator() (Rng &g, const param_type &param)
	Return normal distribution value specified by given parameters. More...
bool	operator== (const TabulatedNormalDistribution< RealType, tableBits > &x) const
	Check if two tabulated normal distributions have identical states. More...
bool	operator!= (const TabulatedNormalDistribution< RealType, tableBits > &x) const
	Check if two tabulated normal distributions have different states. More...

Static Public Member Functions
static std::array< RealType, 1 << tableBits >	makeTable ()
	Fill the table with values for the normal distribution. More...

Constructor & Destructor Documentation

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

gmx::TabulatedNormalDistribution< RealType, tableBits >::TabulatedNormalDistribution ( result_type  mean = 0.0, result_type  stddev = 1.0  )

inlineexplicit

Construct new normal distribution with specified mean & stdddev.

Parameters

mean	Mean value of tabulated normal distribution
stddev	Standard deviation of tabulated normal distribution

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

gmx::TabulatedNormalDistribution< RealType, tableBits >::TabulatedNormalDistribution ( const param_type &  param )

inlineexplicit

Construct new normal distribution from parameter type.

Parameters

param

Parameter class containing mean and standard deviation.

Member Function Documentation

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

static std::array<RealType, 1 << tableBits> gmx::TabulatedNormalDistribution< RealType, tableBits >::makeTable ( )

inlinestatic

Fill the table with values for the normal distribution.

This routine returns a new a std::array with the table data.

This routine is used to help construct objects of this class, and is exposed only to permit testing. Normal code should not need to call this function.

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

result_type gmx::TabulatedNormalDistribution< RealType, tableBits >::max ( ) const

inline

Largest value that can be generated in normal distribution.

Note

The largest value is not infinity with a table, but it depends on the table resolution. With 14 bits, this is roughly four standard deviations above the mean.

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

result_type gmx::TabulatedNormalDistribution< RealType, tableBits >::min ( ) const

inline

Smallest value that can be generated in normal distributon.

Note

The smallest value is not -infinity with a table, but it depends on the table resolution. With 14 bits, this is roughly four standard deviations below the mean.

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

bool gmx::TabulatedNormalDistribution< RealType, tableBits >::operator!= ( const TabulatedNormalDistribution< RealType, tableBits > &  x ) const

inline

Check if two tabulated normal distributions have different states.

Parameters

x	Instance to compare with.

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

template<class Rng >

result_type gmx::TabulatedNormalDistribution< RealType, tableBits >::operator() ( Rng &  g )

inline

Return normal distribution value specified by internal parameters.

Template Parameters

Rng	Random engine type used to provide uniform random bits.

Parameters

g	Random engine of class Rng. For normal GROMACS usage you likely want to use ThreeFry2x64.

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

template<class Rng >

result_type gmx::TabulatedNormalDistribution< RealType, tableBits >::operator() ( Rng &  g, const param_type &  param  )

inline

Return normal distribution value specified by given parameters.

Template Parameters

Rng	Random engine type used to provide uniform random bits.

Parameters

g	Random engine of class Rng. For normal GROMACS usage you likely want to use ThreeFry2x64.
param	Parameters used to specify normal distribution.

template<class RealType = real, unsigned int tableBits = detail::c_TabulatedNormalDistributionDefaultBits>

bool gmx::TabulatedNormalDistribution< RealType, tableBits >::operator== ( const TabulatedNormalDistribution< RealType, tableBits > &  x ) const

inline

Check if two tabulated normal distributions have identical states.

Parameters

x	Instance to compare with.

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

• src/gromacs/random/tabulatednormaldistribution.h
• src/gromacs/random/tabulatednormaldistribution.cpp