Documentation of selrws

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Function Synopsis

NewChromIx = selrws(FitnV, Nsel, Dummy);

Help text

 SELection by Roulette Wheel Selection

 This function performs selection with Roulette wheel selection.
 This function selects a given number of individuals Nsel from a
 population. FitnV is a column vector containing the fitness
 values of the individuals in the population.

 Syntax:  NewChrIx = selrws(FitnV, Nsel)

 Input parameters:
    FitnV     - Column vector containing the fitness values of the
                individuals in the population.
    Nsel      - Number of individuals to be selected

 Output parameters:
    NewChromIx- Column vector containing the indexes of the selected
                individuals relative to the original population, shuffeld.
                The new population, ready for mating, can be obtained
                by calculating OldChrom(NewChromIx,:).

 See also: selection, selsus, sellocal, seltrunc, seltour

Cross-Reference Information

Listing of function selrws

% Author:   Hartmut Pohlheim
% History:  31.05.95    file created
%           03.07.97    function reworked, selection algorithm 
%                          made quicker and easier to understand
%           03.09.98    special case of selection from just one fitness 
%                          value is handled now


function NewChromIx = selrws(FitnV, Nsel, Dummy);

% Identify the population size (Nind)
   [Nind,ans] = size(FitnV);

% Perform selection (roulette wheel selection)
% (often called Stochastic Sampling with Replacement)
   if Nind == 1,
      NewChromIx = repmat(FitnV, [Nsel, 1]);
   else
      CumFitn  = cumsum(FitnV);
      Trials = CumFitn(Nind) .* rand(1, Nsel);
      MatFitn   = repmat(CumFitn, [1, Nsel]);
      MatTrials = repmat(Trials, [Nind, 1]);
      NewChromIx = sum(MatTrials >= MatFitn)+1;
      NewChromIx = NewChromIx(:);
   end

% Shuffle selected values
   [ans, shuf] = sort(rand(Nsel, 1));
   NewChromIx = NewChromIx(shuf);


% End of function