Ant Colony System for the TSP (Matlab Code)

function [BestTourLength,BestTour] = ACSTSP(distances_matrix,number_of_ants,MaxIterations,alpha,beta,rho,target_length)


%AntColonySystem for theTSP
%
%ACSTSP(distances_matrix,number_of_ants,MaxIterations,alpha,beta,rho,target_length)
%
%distances_matrix:symmericreal(NrOfNodesxNrOfNodes) - matrixcontainingdistances
%betweenallnodes:d[i,i] = 0 ,d[i,j] = d[j,i]
%MaxIterations:maximumnumberofiterations to run
%target_length: if atour is found with lessthantarget_length,the function returns
%stops and returnsthistour.
%
%parameterstandardvalues:
%number_of_ants = NrOfNodes
%alpha = 1
%beta = 9
%rho = 0.9
%
%returns[BestTourLength,BestTour]


clc;


loaddistances_matrix.mat
%d = distances_matrix;%defined
d = dis;
n = max(size(d));
%m = number_of_ants;
m = 48 ;
%t_max = MaxIterations;
t_max = 100 ;
%L_target = target_length;
L_target = 32000 ;


alpha = 1
beta = 9
rho = 0.9


%[L_nn,P_nn] = NearestNeighborTSP(d);


L_best = inf;
T_best = 0 ;


%INITIALIZATION ===========================================================


%pheromonetrails
%c = 1 / (n * L_nn);
c = 10 ^- 6 ;
tau = ones(n,n) * c;


%placemantsinnnodes
ant_tours = zeros(m,n + 1 );
ant_tours(:, 1 ) = randint(m, 1 ,[ 1 , 48 ]);


t = 1 ;
while ((t <= t_max) & (L_target < L_best))


%CREATETOURS =============================================================


for s = 2 :n
for k = 1 :m
current_node = ant_tours(k,s - 1 );
visited = ant_tours(k,:);
to_visit = setdiff([ 1 :n],visited);
c_tv = length(to_visit);
p = zeros( 1 ,c_tv);
for i = 1 :c_tv
p(i) = (tau(current_node,to_visit(i))) ^ alpha * ( 1 / d(current_node,to_visit(i))) ^ beta;
end
sum_p = sum(p);
p = p / sum_p;
for i = 2 :c_tv
p(i) = p(i) + p(i - 1 );
end
r = rand;
select = to_visit(c_tv);
for i = 1 :c_tv
if (r <= p(i))
select = to_visit(i);
break;
end
end
city_to_visit = select ;
ant_tours(k,s) = city_to_visit;
tau(current_node,city_to_visit) = ( 1 - rho) * tau(current_node,city_to_visit) + c;
end
end


%UPDATE ===================================================================


ant_tours(:,n + 1 ) = ant_tours(:, 1 );
L_T = zeros( 1 ,m);
best_ant = 1 ;
for k = 1 :m
P = ant_tours(k,:);
L = 0 ;
for i = 1 :n
L = L + d(P(i),P(i + 1 ));
end
L_T(k) = L;
if (L_T(k) < L_T(best_ant))
best_ant = k;
end
end
L_min = min(L_T);
T_min = ant_tours(best_ant,:);


%updatepheromonetrails;
for i = 1 :n
tau(T_min(i),T_min(i + 1 )) = ( 1 - rho) * tau(T_min(i),T_min(i + 1 )) + rho / L_min;
end


%COMPLETE ================================================================
clc;
t = t + 1
current_cities = ant_tours(:,n);
ant_tours = zeros(m,n + 1 );
ant_tours(:, 1 ) = current_cities;
if (L_min < L_best)
L_best = L_min;
T_best = T_min;
end
L_best


end %ends while


clc;
t
BestTourLength = L_best
BestTour = T_best