How to apply a algebraic function to n number of arrays in a template?

Hello everyone. I am working on Particle Swarm Optimisation(PSO) and am new to matlab. I am facing problem in applying algebraic calculations to the elements of array placed in template. Can anyone please let me know how to resolve this. I am providing my code below. The problem is at particle(it,i).VelChange and particle(it,i).VelSigmoid. Am not able to get any values in these two.

The following is my code:

clc;
clear;
close all;

[D, A, C] = problem3();

MaxIt=2;
nPop=2;

VMx=4;
VMn=-4;
c1=0.5;
c2=0.5;
r1=0.5;
r2=0.5;

CostHandle = @(SOLN) calc3(SOLN);

empty_particle.Sol = [];
empty_particle.Cost = [];
empty_particle.Velocity = [];
empty_particle.VelSigmoid = [];
empty_particle.VelChange = [];
empty_particle.Best.Sol = [];
empty_particle.Best.Cost = [];

particle=repmat(empty_particle,nPop,1);

GlobalBest.Cost=inf;

for i=1:nPop 

      % RANDOM SOLUTION
      particle(i).Sol=solution3(D, A, C);

      % PARTICLE VELOCITIES
      particle(i).Velocity=VMx+(VMn-VMx).*rand(A,C);    

      % COST CALCULATION
      particle(i).Cost=CostHandle(particle(i).Sol);

      % ASSIGNING PERSONAL BEST
      particle(i).Best.Sol=particle(i).Sol;
      particle(i).Best.Cost=particle(i).Cost;

      % ASSIGNING GLOBAL BEST
       if particle(i).Best.Cost<GlobalBest.Cost
          GlobalBest=particle(i).Best;
      end

end

for it=1:MaxIt

      for i=1:nPop

          particle(it,i).VelChange= (c1*r1.*(particle(it,i).Best.Sol-particle(it,i).Sol) ...
                                            +c2*r2.*(GlobalBest(it,i)-particle(it,i).Sol));

           particle(it,i).VelSigmoid=(1./1+exp([particle(i).Velocity]));

      end
  end

BestCosts=zeros(MaxIt,1);
BestCosts=GlobalBest;