gbest(it,:)=gbest(it-1,:);
        gbestcost(it)=gbestcost(it-1);
        for i=1:npop
            particle(i).velocity=w*particle(i).velocity...
                                +c1*rand*(particle(i).pbest-particle(i).position)...
                                +c2*rand*(gbest(it,:)-particle(i).position);
                            
            particle(i).velocity=min(max(particle(i).velocity,-vmax),vmax);
            
            particle(i).position=particle(i).position+particle(i).velocity;
            
            particle(i).position=min(max(particle(i).position,xmin),xmax);
            
            particle(i).cost=Cost(particle(i).position);