How to resolve Matlab error: Cell contents reference from a non-cell array object.; while solving tsp using particle swarm optimization

function scores = traveling_salesman_fitness(x,distances)
%TRAVELING_SALESMAN_FITNESS  Custom fitness function for TSP.
%   SCORES = TRAVELING_SALESMAN_FITNESS(X,DISTANCES) Calculate the fitness
%   of an individual. The fitness is the total distance traveled for an
%   ordered set of cities in X. DISTANCE(A,B) is the distance from the city
%   A to the city B.

   scores = zeros(size(x,1),1);

   for j = 1:size(x,1)
    % here is where the special knowledge that the population is a cell
    % array is used. Normally, this would be pop(j,:);
    p = abs(x{j}); % HERE APPEARS THE ERROR

    f = distances((p(end)),(p(1)));
     for i = 2:length(p)
        f = f + distances(p(i-1),p(i));
     end
    scores(j) = f;
  end

Answer 1

[Walter Roberson]

There is nothing in what you show that would establish for us that x will be a cell array when it is passed in. We need to see how it is constructed.