Error: The variable Agent in a parfor cannot be classified

parfor ii = 1:Workspace.Number_of_Compartments
    Comp(ii).Vehicles = zeros(length(Compartment(ii).Vehicles),2)
    for jj = 1:length(Compartment(ii).Vehicles)
        Veh_ID = Compartment(ii).Vehicles(jj);
        for zz = 1:length(Agent(Veh_ID).Structure.Following_Compartment)
            if (Agent(Veh_ID).Structure.Following_Compartment(zz) == ...
                    Agent(Veh_ID).Structure.Current_Compartment)
                Agent(Veh_ID).Structure.Local_Task = [Agent(Veh_ID).Structure.Local_Task,...
                    Agent(Veh_ID).Structure.Global_Task_Zones(zz)];
            else
                cur_comp = Agent(Veh_ID).Structure.Current_Compartment;
                fol_comp = Agent(Veh_ID).Structure.Following_Compartment(zz);
                Find1 = find(Compartment(cur_comp).Following_Compartment == fol_comp);
                % All elements of the Find1 row of the field Exite_Nodes of
                % the Compartment(cur_comp)
                Find2 = Compartment(cur_comp).Exite_Nodes(Find1,:);
                Find2_1 = find(Find2 ~= 0);
                Find3 = find(Compartment(cur_comp).Exite_Nodes_State(Find1,:) == 0);
                Find4 = intersect(Find2_1,Find3);
                Find4 = Find4(randi(length(Find4)));
                Agent(Veh_ID).Structure.Local_Task = [Agent(Veh_ID).Structure.Local_Task,...
                    Find2(Find4)];
            end
        end
    end

How to eliminate this error? I need to add data in the structure inside parfor loop.

Answer 1

[Jemima Pulipati]

Hello,

From my understanding, you are using the 'Agent' variable for slicing as well as indexing and trying to assign a value to it. This error arises because once you index a variable you cannot use it anywhere else in the parfor loop.

This has been mentioned in Solve Variable Classification Issues in parfor-Loops.

The suggested workaround would be to use a temporary variable inside the for loops and one 'Agent' variable that gets assigned the required values in the main parfor loop. In this way the variable 'Agent' would be referenced only once in the entire parfor loop.

Some answers from the community which might be of relevance to you are:

https://www.mathworks.com/matlabcentral/answers/147075-parfor-loop-variable-cannot-be-classified

https://www.mathworks.com/matlabcentral/answers/415859-error-the-variable-in-a-parfor-cannot-be-classified

https://www.mathworks.com/matlabcentral/answers/318771-how-to-overcome-this-error-variable-in-a-parfor-cannot-be-classified

https://www.mathworks.com/matlabcentral/answers/268894-variable-in-parfor-cannot-be-classified