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% MIGRATE.M (MIGRATion of individuals between subpopulations)
%
% This function performs migration of individuals.
%
% Syntax: [Chrom, ObjV] = migrate(Chrom, SUBPOP, MigOpt, ObjV)
%
% Input parameters:
% Chrom - Matrix containing the individuals of the current
% population. Each row corresponds to one individual.
% SUBPOP - Number of subpopulations
% MigOpt - (optional) Vector containing migration parameters
% MigOpt(1): MIGR - Rate of individuals to be migrated per
% subpopulation (% of subpopulation)
% if omitted or NaN, 0.2 (20%) is assumed
% MigOpt(2): Select - number indicating the selection method
% of replacing individuals
% 0 - uniform selection
% 1 - fitness-based selection (replace worst
% individuals)
% if omitted or NaN, 0 is assumed
% MigOpt(3): Structure - number indicating the structure
% of the subpopulations for migration
% 0 - net structure (unconstrained migration)
% 1 - neighbourhood structure
% 2 - ring structure
% if omitted or NaN, 0 is assumed
% ObjV - (optional) Column vector containing the objective values
% of the individuals in the current population, needed for
% fitness-based migration, this saves the
% recalculation of objective values for population.
%
% Output parameters:
% Chrom - Matrix containing the individuals of the current
% population after migration.
% ObjV - if ObjV is input parameter, than column vector containing
% the objective values of the individuals of the current
% generation after migration.
%
% Author: Hartmut Pohlheim
% History: 16.02.94 file created
% 18.02.94 comments at the beginning added
% exchange of ObjV too
% 25.02.94 clean up
% 26.02.94 ObjV optional input parameter
% Select and Structure added, parameter reordered
% 17.03.94 renamed to migrate.m, more parameter checks
% 20.01.03 tested under MATLAB v6 by Alex Shenfield
function [Chrom, ObjV] = migrate(Chrom, SUBPOP, MigOpt, ObjV);
% Check parameter consistency
if nargin < 2, error('Input parameter SUBPOP missing'); end
if (nargout == 2 & nargin < 4), error('Input parameter ObjV missing'); end
[Nind, Nvar] = size(Chrom);
if length(SUBPOP) ~= 1, error('SUBPOP must be a scalar'); end
if SUBPOP == 1, return; end
if (Nind/SUBPOP) ~= fix(Nind/SUBPOP), error('Chrom and SUBPOP disagree'); end
NIND = Nind/SUBPOP; % Compute number of individuals per subpopulation
if nargin > 3,
[mO, nO] = size(ObjV);
if nO ~= 1, error('ObjV must be a column vector'); end
if Nind ~= mO, error('Chrom and ObjV disagree'); end
IsObjV = 1;
else IsObjV = 0; ObjV = [];
end
if nargin < 3, MIGR = 0.2; Select = 0; Structure = 0; end
if nargin > 2,
if isempty(MigOpt), MIGR = 0.2; Select = 0; Structure = 0;
elseif isnan(MigOpt), MIGR = 0.2; Select = 0; Structure = 0;
else
MIGR = NaN; Select = NaN; Structure = NaN;
if length(MigOpt) > 3, error('Parameter MigOpt is too long'); end
if length(MigOpt) >= 1, MIGR = MigOpt(1); end
if length(MigOpt) >= 2, Select = MigOpt(2); end
if length(MigOpt) >= 3, Structure = MigOpt(3); end
if isnan(MIGR), MIGR =0.2; end
if isnan(Select), Select = 0; end
if isnan(Structure), Structure = 0; end
end
end
if (MIGR < 0 | MIGR > 1), error('Parameter for migration rate must be a scalar in [0 1]'); end
if (Select ~= 0 & Select ~= 1), error('Parameter for selection method must be 0 or 1'); end
if (Structure < 0 | Structure > 2), error ('Parameter for structure must be 0, 1 or 2'); end
if (Select == 1 & IsObjV == 0), error('ObjV for fitness-based migration needed');end
if MIGR == 0, return; end
MigTeil = max(floor(NIND * MIGR), 1); % Number of individuals to migrate
% Perform migration between subpopulations --> create a matrix for migration
% in every subpopulation from best individuals of the other subpopulations
% Clear storing matrices
ChromMigAll = [];
if IsObjV == 1, ObjVAll = []; end
% Create matrix with best/uniform individuals of all subpopulations
for irun = 1:SUBPOP
% sort ObjV of actual subpopulation
if Select == 1, % fitness-based selection
[Dummy, IndMigSo]=sort(ObjV((irun-1)*NIND+1:irun*NIND));
else % if Select == 0 % uniform selection
[Dummy, IndMigSo]=sort(rand(NIND, 1));
end
% take MigTeil (best) individuals, copy individuals and objective values
IndMigTeil=IndMigSo(1:MigTeil)+(irun-1)*NIND;
ChromMigAll = [ChromMigAll; Chrom(IndMigTeil,:)];
if IsObjV == 1, ObjVAll = [ObjVAll; ObjV(IndMigTeil,:)]; end
end
% perform migration
for irun = 1:SUBPOP
ChromMig = ChromMigAll;
if IsObjV == 1, ObjVMig = ObjVAll; end
if Structure == 1, % neighbourhood
% select individuals of neighbourhood subpopulations for ChromMig and ObjVMig
popnum = [SUBPOP 1:SUBPOP 1];
ins1 = popnum(irun); ins2 = popnum(irun + 2);
InsRows = [(ins1-1)*MigTeil+1:ins1*MigTeil (ins2-1)*MigTeil+1:ins2*MigTeil];
ChromMig = ChromMig(InsRows,:);
if IsObjV == 1, ObjVMig = ObjVMig(InsRows,:); end
elseif Structure == 2, % ring
% select individuals of actual-1 subpopulation for ChromMig and ObjVMig
popnum = [SUBPOP 1:SUBPOP 1];
ins1 = popnum(irun);
InsRows = (ins1-1)*MigTeil+1:ins1*MigTeil;
ChromMig = ChromMig(InsRows,:);
if IsObjV == 1, ObjVMig = ObjVMig(InsRows,:); end
else % if Structure == 0, % complete net
% delete individuals of actual subpopulation from ChromMig and ObjVMig
DelRows = (irun-1)*MigTeil+1:irun*MigTeil;
ChromMig(DelRows,:) = [];
if IsObjV == 1, ObjVMig(DelRows,:) = []; end
end
% Create an index from a sorted vector with random numbers
[Dummy,IndMigRa]=sort(rand(size(ChromMig,1),1));
% Take MigTeil numbers from the random vector
IndMigN=IndMigRa((1:MigTeil)');
% copy MigTeil individuals into Chrom and ObjV
Chrom((1:MigTeil)+(irun-1)*NIND,:) = ChromMig(IndMigN,:);
if IsObjV == 1, ObjV((1:MigTeil)+(irun-1)*NIND,:) = ObjVMig(IndMigN,:); end
end
% End of function