A container for the symbols used by the GP engine. More...

#include <symbol_set.h>

Public Types
using	weight_t = unsigned

Public Member Functions
category_t	categories () const

void	clear ()
	Clears the current symbol set. More...

symbol *	decode (const std::string &) const

symbol *	decode (opcode_t) const

bool	enough_terminals () const
	We want at least one terminal for every used category. More...

template<class S , class ... Args>
symbol *	insert (Args &&... args)
	Adds a symbol to the symbol set. More...

template<class S , class ... Args>
symbol *	insert (Args &&...)

symbol *	insert (std::unique_ptr< symbol >, double=1.0)
	Adds a new symbol to the set. More...

bool	is_valid () const

const symbol &	roulette (category_t) const
	Extracts a random symbol from the symbol set without bias between terminals and functions . More...

const symbol &	roulette_free (category_t) const
	Extracts a random symbol from the symbol set. More...

const function &	roulette_function (category_t) const

const terminal &	roulette_terminal (category_t) const

	symbol_set ()
	Sets up the object. More...

std::size_t	terminals (category_t) const

weight_t	weight (const symbol &) const

Friends
std::ostream &	operator<< (std::ostream &, const symbol_set &)
	Prints the symbol set to an output stream. More...

Detailed Description

A container for the symbols used by the GP engine.

Symbols are stored to be quickly recalled by category and randomly selected.

Note: The functions and terminals used should be powerful enough to be able to represent a solution to the problem. On the other hand, it's better not to use a symbol set too large (this enlarges the search space and makes harder the search for a solution).

Definition at line 36 of file symbol_set.h.

Member Typedef Documentation

◆ weight_t

using vita::symbol_set::weight_t = unsigned

Definition at line 39 of file symbol_set.h.

Constructor & Destructor Documentation

◆ symbol_set()

vita::symbol_set::symbol_set ( )

Sets up the object.

The constructor allocates memory for up to k_args arguments.

Definition at line 27 of file symbol_set.cc.

Member Function Documentation

◆ categories()

category_t vita::symbol_set::categories ( ) const

Returns: number of categories in the symbol set (>= 1)

See also: category_set::size().

Definition at line 214 of file symbol_set.cc.

◆ clear()

void vita::symbol_set::clear ( )

Clears the current symbol set.

Definition at line 35 of file symbol_set.cc.

◆ decode() [1/2]

symbol * vita::symbol_set::decode ( const std::string & dex ) const

Parameters

[in] dex the name of a symbol

Returns: a pointer to the symbol identified by dex (0 if not found)

Attention: Please note that opcodes are automatically generated and fully identify a symbol (they're primary keys). Conversely the name of a symbol is chosen by the user, so, if you don't pay attention, different symbols may have the same name.

Definition at line 198 of file symbol_set.cc.

◆ decode() [2/2]

symbol * vita::symbol_set::decode ( opcode_t opcode ) const

Parameters

[in] opcode numerical code used as primary key for a symbol

Returns: a pointer to the vita::symbol identified by opcode (nullptr if not found).

Definition at line 179 of file symbol_set.cc.

◆ enough_terminals()

bool vita::symbol_set::enough_terminals ( ) const

We want at least one terminal for every used category.

Returns: true if there are enough terminals for secure individual generation

Definition at line 235 of file symbol_set.cc.

◆ insert() [1/2]

template<class S , class ... Args>

symbol * vita::symbol_set::insert ( Args &&... args )

Adds a symbol to the symbol set.

Template Parameters

S	symbol to be added

Parameters

[in] args arguments used to build S

Returns: a raw pointer to the symbol just added (or nullptr in case of error)

Insert a symbol in the symbol set without the user having to allocate memory.

Note: Only partially replaces the insert(std::unique_ptr) method (e.g. building from factory).

Remarks: Assumes a standard frequency (1.0) for symbol S.

Definition at line 167 of file symbol_set.h.

◆ insert() [2/2]

symbol * vita::symbol_set::insert	(	std::unique_ptr< symbol >	s,
		double	wr = `1.0`
	)

Adds a new symbol to the set.

Parameters

[in]	s	symbol to be added
[in]	wr	the weight of `s` (`1.0` means standard frequency, `2.0` double probability of selection)

Returns: a raw pointer to the symbol just added (or nullptr in case of error)

A symbol with undefined category will be changed to the first free category.

Definition at line 55 of file symbol_set.cc.

◆ is_valid()

bool vita::symbol_set::is_valid ( ) const

Returns: true if the object passes the internal consistency check

Definition at line 307 of file symbol_set.cc.

◆ roulette()

const symbol & vita::symbol_set::roulette ( category_t c ) const

Extracts a random symbol from the symbol set without bias between terminals and functions .

Parameters

[in] c a category

Returns: a random symbol of category c

Attention

$P(terminal_i|terminal) = \frac{w_i}{\sum_{t \in terminals} w_t}$
$P(function_i|function) = \frac{w_i}{\sum_{f \in functions} w_f}$

Note: If all symbols have the same probability to appear into a chromosome, there could be some problems. For instance, if our problem has many variables (let's say 100) and the function set has only 4 symbols we cannot get too complex trees because the functions have a reduced chance to appear in the chromosome (e.g. it happens in the Forex example).

See also: https://github.com/morinim/vita/wiki/bibliography#1

Definition at line 143 of file symbol_set.cc.

◆ roulette_free()

const symbol & vita::symbol_set::roulette_free ( category_t c ) const

Extracts a random symbol from the symbol set.

Parameters

[in] c a category

Returns: a random symbol of category c

Attention

Given $S_t = \sum_{i \in terminals} {w_i}$ and $S_f = \sum_{i \in functions} {w_i}$ we have:

$P(terminal_i|terminal) = \frac {w_i} {S_t}$
$P(function_i|function) = \frac {w_i} {S_f}$
$P(terminal) = \frac {S_t} {S_t + S_f}$
$P(function) = \frac {S_f} {S_t + S_f}$

Definition at line 168 of file symbol_set.cc.

◆ roulette_function()

const function & vita::symbol_set::roulette_function ( category_t c ) const

Parameters

[in] c a category

Returns: a random function of category c

Definition at line 101 of file symbol_set.cc.

◆ roulette_terminal()

const terminal & vita::symbol_set::roulette_terminal ( category_t c ) const

Parameters

[in] c a category

Returns: a random terminal of category c

Definition at line 113 of file symbol_set.cc.

◆ terminals()

std::size_t vita::symbol_set::terminals ( category_t c ) const

Parameters

[in] c a category

Returns: number of terminals in category c

Definition at line 223 of file symbol_set.cc.

◆ weight()

symbol_set::weight_t vita::symbol_set::weight ( const symbol & s ) const

Parameters

[in] s a symbol

Returns: the weight of s

Definition at line 260 of file symbol_set.cc.

Friends And Related Function Documentation

◆ operator<<

std::ostream & operator<<	(	std::ostream &	,
		const symbol_set &
	)

friend

Prints the symbol set to an output stream.

Parameters

[out]	o	output stream
[in]	ss	symbol set to be printed

Returns: output stream including ss

Note: Useful for debugging purpose.

Definition at line 278 of file symbol_set.cc.

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

Public Types

Public Member Functions

Friends

Detailed Description

Member Typedef Documentation

◆ weight_t

Constructor & Destructor Documentation

◆ symbol_set()

Member Function Documentation

◆ categories()

◆ clear()

◆ decode() [1/2]

◆ decode() [2/2]

◆ enough_terminals()

◆ insert() [1/2]

◆ insert() [2/2]

◆ is_valid()

◆ roulette()

◆ roulette_free()

◆ roulette_function()

◆ roulette_terminal()

◆ terminals()

◆ weight()

Friends And Related Function Documentation

◆ operator<<