Documentation of mutbmd

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Function Synopsis

NewChrom = mutbmd(Chrom, VLUB, MutOpt);

Help text

 real value Mutation like Discrete Breeder genetic algorithm

 This function takes a matrix Chrom containing the real
 representation of the individuals in the current population,
 mutates the individuals with probability MutR and returns
 the resulting population.

 This function implements the mutation operator of the Breeder
 Genetic Algorithm. (Muehlenbein et. al.)

 Syntax:  NewChrom = mutbmd(OldChrom, VLUB, MutOpt)

 Input parameter:
    Chrom     - Matrix containing the chromosomes of the old
                population. Each row corresponds to one individual.
    VLUB      - Matrix describing the boundaries of each variable.
    MutOpt    - (optional) Vector containing mutation options
                MutOpt(1): MutRate - number containing the mutation rate -
                           probability for mutation of a variable
                           if omitted or NaN, MutRate = 1/variables per individual
                           is assumed
                MutOpt(2): MutRange - (optional) number for shrinking the
                           mutation range in the range [0 1], possibility to
                           shrink the range of the mutation depending on,
                           for instance actual generation.
                           if omitted or NaN, MutRange = 1 is assumed
                MutOpt(3): MutPreci - (optional) precision of mutation steps
                           if omitted or NaN, MutPreci = 16 is assumed

 Output parameter:
    NewChrom  - Matrix containing the chromosomes of the population
                after mutation in the same format as OldChrom.

 See also: mutate, mutbin, mutint

Listing of function mutbmd

% Author:   Hartmut Pohlheim
% History:  23.11.94    file created
%           06.12.94    change of function name
%                       check of boundaries after mutation out of loop
%           16.02.95    preparation for multi-subpopulations at once
%           03.03.95    Lower and Upper directly used (less memory)
%           19.03.95    multipopulation support removed
%                       more parameter checks
%           27.03.95    Delta exact calculated, for loop saved
%           17.01.96    Parameter MutPreci added
%           02.03.98    excluded setting of variables to boundaries, 
%                          when variables outside boundaries
%           25.08.98    changed default value of MutRange to 0.2 (from 1)


function NewChrom = mutbmd(Chrom, VLUB, MutOpt);

% Identify the population size (Nind) and the number of variables (Nvar)
   [Nind,Nvar] = size(Chrom);

% Set standard mutation parameter
   MutOptStandard = [1/Nvar, 0.2, 16];      % MutRate = 1/Nvar, MutRange = 1, MutPreci = 16

% Check parameter consistency
   if nargin < 2,  error('Not enough input parameter'); end

   [mF, nF] = size(VLUB);
   if mF ~= 2, error('VLUB must be a matrix with 2 rows'); end
   if Nvar ~= nF, error('VLUB and Chrom disagree'); end

   if nargin < 3, MutOpt = []; end
   if isnan(MutOpt), MutOpt = []; end
   if length(MutOpt) > length(MutOptStandard), error(' Too many parameter in MutOpt'); end

   MutOptIntern = MutOptStandard; MutOptIntern(1:length(MutOpt)) = MutOpt;
   MutRate = MutOptIntern(1); MutRange = MutOptIntern(2); MutPreci = MutOptIntern(3);

   if isnan(MutRate), MutRate = MutOptStandard(1);
   elseif (MutRate < 0 | MutRate > 1), error('Parameter for mutation rate must be a scalar in [0, 1]'); end

   if isnan(MutRange), MutRange = MutOptStandard(2);
   elseif (MutRange < 0 | MutRange > 1), 
      error('Parameter for shrinking mutation range must be a scalar in [0, 1]');
   end

   if isnan(MutPreci), MutPreci = MutOptStandard(3);
   elseif MutPreci <= 1, error('Parameter for mutation precision must be greater than 1'); end

% the variabels are mutated with probability MutRate
% NewChrom = Chrom (+ or -) * Range * MutRange * Delta
% Range = 0.5 * (upperbound - lowerbound)
% Delta = Sum(Alpha_i * 2^-i) from 0 to MutPreci; Alpha_i = rand(MutPreci,1) < 1/MutPreci

% Matrix with range values for every variable
   Range = repmat(MutRange * (VLUB(2,:) - VLUB(1,:)), [Nind 1]);

% zeros and ones for mutation or not of this variable, together with Range
   Range = Range .* (rand(Nind,Nvar) < MutRate);

% Compute, if + or - sign 
   Range = Range .* (1 - 2 * (rand(Nind,Nvar) < 0.5));

% Used for later computing, here only ones computed
   Vect = 2 .^ (-(0:(MutPreci-1))');
   Delta = (rand(Nind,MutPreci) < 1/MutPreci) * Vect;
   Delta = repmat(Delta, [1 Nvar]);

% Perform mutation 
   NewChrom = Chrom + Range .* Delta;


% End of function