Re: [jgap-users] BestChromosomesSelector and WeightedRouletteSelectorquestion

[Klaus M. <jg...@kl...>]

Krzysztof,
 
to your first question: In method add(IChromosome a_chromosomeToAdd), which
has to be called before any selection can take place, the last line is:
    // Indicate that the list of chromosomes to add needs sorting.
    // -----------------------------------------------------------
    m_needsSorting = true;

By this, the sorting procedure is activated.
 
Your second question regarding WeightedRouletteSelector:
The number of spins is determined by the JGAP core. The method to do this
is:
  public synchronized void selectChromosomes(int a_howManyToSelect,
Population a_to_pop) {... }

Best

Klaus
www.klaus-meffert.com <http://www.klaus-meffert.com/> 

 


  _____  

From: Krzysztof Chmielewski [mailto:krz...@gm...] 
Sent: Tuesday, December 22, 2009 3:02 AM
To: jga...@li...
Subject: [jgap-users] BestChromosomesSelector and
WeightedRouletteSelectorquestion


Hi everyone. Thank You very much for helping me in my last JGAP
question/trouble :). 

Yet I have another question... this time I have some doubts about
BestChromosomeSelector and WeightedRouletteSelector.

In JGAP documentation we can reed that: 
"Implementation of a NaturalSelector that takes the top n chromosomes into
the next generation. n can be specified. Which chromosomes are the best is
decided by evaluating their fitness value."

So I looked to the code of that class and DefaultConfiguration  code, and
there is something like that:

DefaultConfiguration code:
BestChromosomesSelector bestChromsSelector = new
BestChromosomesSelector(this, 0.90d);

BestChromosomesSelector code:
  public BestChromosomesSelector(final Configuration a_config,   final
double a_originalRate)
      throws InvalidConfigurationException {
    super(a_config);
    m_chromosomes = new Population(a_config);
    m_needsSorting = false; <- this part give me some doubts
    setDoubletteChromosomesAllowed(true);
    setOriginalRate(a_originalRate);
    m_fitnessValueComparator = new FitnessAgeValueComparator();
  }

m_needsSorting tells JGAP that, is there need to sort the incoming
population by Fitness Value, right? 


Further in the BestChromosomeSelector ther is a function that select n
chromosomes:
  public void selectChromosomes(final int a_howManyToSelect, Population
a_to_pop)
.
.some code
.    
// Sort the collection of chromosomes previously added for evaluation.
    // Only do this if necessary.
    // -------------------------------------------------------------------
    if (m_needsSorting) {
      Collections.sort(m_chromosomes.getChromosomes(),
                       m_fitnessValueComparator);
      m_needsSorting = false;
    }
    // To select a chromosome, we just go thru the sorted list.
    // --------------------------------------------------------
    IChromosome selectedChromosome;
    for (int i = 0; i < canBeSelected; i++) {
      selectedChromosome = m_chromosomes.getChromosome(i);
      selectedChromosome.setIsSelectedForNextGeneration(true);
      a_to_pop.addChromosome(selectedChromosome);
    }
.
some other code
.
.

But if we do not sort the list... we will not get TOP n chromosomes. We will
get only first/last n chromosomes from the list. So why there is no
m_deedsSorting = true in DefaultConfiguration , or why in
BestChromosomesSelector code we have m_needsSorting = false? Where I can
change this?


My  next question  is  about  WeightedRouletteSelector. In JGAP
documentation we can reed that: 
Then the wheel is spun again and again until the requested number of
Chromosomes have been selected.

But there is no parameter to determine the number of spun. The class
constructors are:
WeightedRouletteSelector(), and WeightedRouletteSelector(Configuration). So
where I can set the number of spuns, where I can define how many chromosomes
goes to next evolution. 

Ok, so going next... the basic calculation of number of slots (or
probability of selection) in roulette wheel  that each chromosome has is
something like that:
fitness_value_of_chromosome_i/sum(fitness_values_off_all_chromosomes). Is it
something like that in JGAP WeightedRouletteSelector or is something
different?

Thank You for any help ;)

Best
Krzysztof