Dot indexing is not supported for variables of this type on a parfor line with no dot indexing.

I have been scratching my head for multiple hours on this one. In evaluation.m, I get an error "Dot indexing is not supported for variables of this type" on line 32, which contains "parfor i = 1:x1". There is absolutely zero dot indexing in this line, and the code runs fine when replacing "parfor" with "for". I want to use parfor because this will significantly speed up the runtime of the code (which takes hours or days).

What is going on, and how can I fix this?

function [Y, g, avgFullTravelTime, scoreFactor]=evaluation(P, numInputs)
% P = population
[x1, y1]=size(P);
H=zeros(1,x1);

Vissim = actxserver('Vissim.Vissim');
path = 'C:\Users\Public\Documents\PTV Vision\PTV Vissim 2022\Pitt Campus\Calibration Network with slopes';
filename = fullfile(path, 'Pitt_Campus_Model_1-6-23(new).inpx');
Vissim.LoadNet(filename, false);

expectedTime = [346,393,479,451,462,494,260,388,145,297,422,311];
measureRange = [48, 49, 50, 52, 54, 57, 59, 61, 65, 66, 67, 68, 69];
% NumberRoute  [1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14, 15
routes = length(expectedTime);
segments = 21;

score = zeros(x1);
scoreFactor = zeros(x1, routes);
avgFullTravelTime = zeros(x1, routes);
g = zeros(x1, routes);
totalTravelTime = zeros(x1, segments);
vehsPerTimeInt = zeros(x1, segments, 3);
avgTTPerTimeInt = zeros(x1, segments, 3);
avgTravelTime = zeros(x1, segments);
for w = 1:segments
   Veh_TT_measurement(w) = Vissim.Net.VehicleTravelTimeMeasurements.ItemByKey(w+47); 
end




parfor i = 1:x1
    tic
    
    vpti1 = zeros(segments, 3);
    attpti1 = zeros(segments, 3);
    ttt1 = zeros(segments);
    tv1 = zeros(segments);
    att1 = zeros(segments);
    aftt1 = zeros(routes);
    g1 = zeros(routes);
    sf1 = zeros(routes);
    
    % rest of code
end

[Matt J]

I get an error "Dot indexing is not supported for variables of this type" on line 32

We need to see the error message copy/pasted. Also, some inputs to the code that we can reproduce the error with would probably help.

[Noah]

I have done what others suggested and put the body of the code in a new function. Now, I get the (copy-pasted) error:

Error using evaluationLoopBody (line 23)
Dot indexing is not supported for variables of this type.

on the line:

Vissim.Net.VehicleInputs.ItemByKey(vin).set('AttValue', 'Volume(1)', amount(vin));

The inputs for the main evaluation function are numInputs, which is currently set to 82, and P, a 48x984 matrix of doubles that are all either 0 or 1.

Answer 1

[Raymond Norris]

My guess is that it has to do with your ActiveX Server, specifically if Veh_TT_measurement is used in your parfor. See if this will help

How can I use COM objects with a "parfor" loop via "actxserver"? - MATLAB Answers - MATLAB Central (mathworks.com)

[Noah]

Here is the code within the parfor loop using dot indexing. Because this indexing is used to interface with another program, I don't know how to remove the dot indexing or change the variable to a supported type.

for vin = 1:numInputs %vehicle input number
        Vissim.Net.VehicleInputs.ItemByKey(vin).set('AttValue', 'Volume(1)', amount(vin));
        Vissim.Net.VehicleInputs.ItemByKey(vin).set('AttValue', 'Volume(2)', amount(vin));
    end
    
    % Run simulation using parameters
    % Delete all previous simulation runs first:
    simRuns = Vissim.Net.SimulationRuns.GetAll; 
    for simRunNo = 1 : length(simRuns)
        Vissim.Net.SimulationRuns.RemoveSimulationRun( simRuns{simRunNo} );
    end
    
    % Activate QuickMode:
    set(Vissim.Graphics.CurrentNetworkWindow, 'AttValue', 'QuickMode', 1);
    Vissim.SuspendUpdateGUI; %  stop updating of the complete Vissim workspace (network editor, list, chart and signal time table windows)
    
    End_of_simulation = 1200;
    set(Vissim.Simulation, 'AttValue', 'SimPeriod', End_of_simulation);
    Sim_break_at = 0; % simulation second [s] => 0 means no break!
    set(Vissim.Simulation, 'AttValue', 'SimBreakAt', Sim_break_at);
    % Set maximum speed:
    set(Vissim.Simulation, 'AttValue', 'UseMaxSimSpeed', true);
    
    for cnt_Sim = 1 : 1
        set(Vissim.Simulation, 'AttValue', 'RandSeed', cnt_Sim);
        Vissim.Simulation.RunContinuous;
    end
    Vissim.ResumeUpdateGUI; % allow updating of the complete Vissim workspace (network editor, list, chart and signal time table windows)
    set(Vissim.Graphics.CurrentNetworkWindow, 'AttValue', 'QuickMode', 0); % deactivate QuickMode

[Raymond Norris]

Did the MATLAB Answer I post help?

[Noah]

This answer is leading me in the right direction. I might ask more questions later, but for now I seem good.

[Raymond Norris]

Good to hear, @Noah

Answer 2

[Edric Ellis]

Unfortunately, error messages from anywhere within a parfor loop are reported as occurring on the line where the loop starts. This is a current limitation of the way parfor works. As a workaround, if you put the entire body of the loop into a separate function, you'll get a more sensible error message.

Almost certainly as @Raymond Norris suggests it is to do with the ActiveX object - if this cannot be saved and loaded correctly, it may show up having the value [] inside the parfor loop, and then you'll end up with the error you posted when you try to apply a dot-reference to it.

[Image Analyst]

Maybe, to debug, put this code inside the parfor loop just before you try to use Vissim the first time:

if isempty(Vissim)
    errorMessage = sprintf('Error: ActiveX server Vissim is empty on iteration #%d!', vin);
    fprintf('%s\n', errorMessage);
    uiwait(errordlg(errorMessage));
    continue; % Skip rest of loop.
end

[Raymond Norris]

parfor won't display the error dialog box. I expect this would hang the MATLAB client.

[Edric Ellis]

Yeah, better to do

assert(~isempty(Vissim), 'Vissim is empty!')