Created by Scott Robert Ladd at Coyote Gulch Productions.
A simulated roulette wheel for weighted selection. More...
#include <roulette.h>
You've probably seen a standard gambler's roulette wheel, a spinning circle divided into thirty-seven or thirty-eight equal-sized, pie-shaped sections. The croupier sets the wheel spinning and at the same time tosses an marble into the bowl in the direction opposite to that in which the wheel is moving; when the motion of the wheel ceases, the ball comes to rest in one of the numbered sections.
As an algorithm, a roulette wheel is an array of weights, and the marble is a random integer less than the sum of all weights in the population. To pick on of the "section" (in this case, an index), the algorithm simulates the bouncing metal ball by iterating through the array of weights; if the marble value is less than the current weight (i.e., the ball has stopped), the algorithm returns the index of that weight. Otherwise, the algorithm subtracts the current weight from the marble value, and repeats the process with the next element in the weight array. Thus the largest weights values tend to be the most likely resting places for the marble, since they use a larger area of the abstract wheel.
libevocosm::roulette_wheel::roulette_wheel | ( | const vector< double > & | a_weights, |
double | a_min_weight = std::numeric_limits< double >::epsilon() , |
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double | a_max_weight = std::numeric_limits< double >::max() |
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) |
Creates a new roulette_wheel based on a set of weights.
a_weights | - A vector of weights defining the wheel |
a_min_weight | - Minimum possible weight value (defaults to epsilon for type) |
a_max_weight | - Maximum possible weight value (defaults to max for type) |
libevocosm::roulette_wheel::roulette_wheel | ( | const double * | a_weights, |
size_t | a_length, | ||
double | a_min_weight = std::numeric_limits< double >::epsilon() , |
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double | a_max_weight = std::numeric_limits< double >::max() |
||
) |
Creates a new roulette_wheel based on a set of weights.
a_weights | - An array of weights defining the wheel |
a_length | - Number of elements in a_weights |
a_min_weight | - Minimum possible weight value (defaults to 1.0) |
a_max_weight | - Maximum possible weight value (defaults to 100.0) |
libevocosm::roulette_wheel::roulette_wheel | ( | const roulette_wheel & | a_source | ) |
Creates a new roulette_wheel from an existing one.
a_source | - The source object |
libevocosm::roulette_wheel::~roulette_wheel | ( | ) |
Destroys a roulette_wheel, freeing resources.
size_t libevocosm::roulette_wheel::get_index | ( | ) | const |
Returns a randomly-selected index value by simulating the bouncing of a ball on a roulette wheel, where each index is a "slot" with a width determined by its assigned weight.
Referenced by libevocosm::machine_tools::mutation_selector::get_index().
size_t libevocosm::roulette_wheel::get_size | ( | ) | const [inline] |
Gets the number of weights indexed by the roulette wheel.
References m_size.
double libevocosm::roulette_wheel::get_weight | ( | size_t | a_index | ) | const |
Gets the weight assigned to a specific index.
a_index | Index for which weight should be returned |
roulette_wheel& libevocosm::roulette_wheel::operator= | ( | const roulette_wheel & | a_source | ) |
Assigns a roulette_wheel the state of another.
a_source | - The source object |
double libevocosm::roulette_wheel::set_weight | ( | size_t | a_index, |
double | a_weight | ||
) |
Changes the weight assigned to a specific wheel index.
a_index | - Index to change |
a_weight | - New weight Value |
Referenced by libevocosm::machine_tools::mutation_selector::set_weight().
© 2011 Scott Robert Ladd. All rights reserved.
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