Issue in using user-defined objects within parfor loop

Question

Davide Fenucci 2017-12-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/373685-issue-in-using-user-defined-objects-within-parfor-loop

编辑： Davide Fenucci 2017-12-19

I'm pretty new to parallel computation in MATLAB and I'm facing the following issue: I have the following script calling iteratively an optimization function

trials = cell2struct([ ...
    {     4      5      6      7     10      16     17     18      23     24}; ...
    {   0.5      1    0.5      0      0     0.5    0.5    0.5     0.5      0}; ...
    {     0      0     pi     pi      0 pi-pi/6  -pi/6   pi/6 pi+pi/6   pi/6}; ...
    {0.0458 0.0440 0.0510 0.0312 0.0464  0.0449 0.0461 0.0598  0.0598 0.0511} ], ...
    {'idx', 'mounting', 'q5_0', 'dq4_squared'}, 1);
coeff = [2, 10.5, 20, 25, 2.5];
while < some_stop_condition >
    [coeff, fval] = fminunc(@(x) EvaluateIndex(x, trials), coeff);
end

I have a working sequential version of the function EvaluateIndex, but since it takes very much time to perform the computation I would like to switch to a parallelized version. A simplified version of the "parallelized" objective function EvaluateIndex is as follows:

function MeanSquaredError = EvaluateIndex(coeff, configs)
    % Simulation time
    dT      = 0.01;                     % Time step [s]
    T_final = 60;                       % Duration  [s]
      % Wave characteristics
      wave = SeaWave( < sea_wave_params > );
      % Vehicle settings
      for i = 1:length(configs)
          vehicle(i) = PrototypeWAVE( < vehicle_i_params > );
      end
      dq4_squared = zeros(1, length(configs));
      tic
      parfor i = 1:length(configs)
           % Initial conditions
           q1_0 = 0;
           q2_0 = 0;
           q3_0 = 0;
           q4_0 = pi/2;
           q5_0 = configs(i).q5_0;
           q_0  = [ q1_0+1.3*(1-cos(q3_0)), q2_0+1.3*sin(q3_0), q3_0, q4_0, q5_0 ]';
           dq_0 = [ 0, 0, 0, 0, 0 ]';
           % Run simulation
           [~, Results] = Run(vehicle(i), wave, [q_0; dq_0], dT, T_final);
           % Get results
           dq4_squared(i) = mean(Results(:,9).^2);
      end
      toc
      MeanSquaredError = sum( (dq4_squared - horzcat(configs.dq4_squared)).^2 );
  end

Here, SeaWave and PrototypeWAVE are two classes, and the function Run is a method of the PrototypeWAVE class. According to some suggestions I have found, I have defined the objects of these classes outside the parfor loop; however, when I try to run the script, I get the following warnings:

Warning: Element(s) of class 'SeaWave' do not match the current constructor definition.  The element(s) have been converted to structures.
Warning: Element(s) of class 'PrototypeWAVE' do not match the current constructor definition.  The element(s) have been converted to structures.

and this error:

Error using EvaluateIndex (line 75)
Cannot find an exact (case-sensitive) match for 'Run'
The closest match is: run in /Applications/MATLAB_R2016b.app/toolbox/matlab/lang/run.m

It seems that MATLAB does not recognize the existence of the classes and their methods. I have already tried to add the line addAttachedFiles(gcp, {'./@SeaWave', './@PrototypeWAVE'}) before the parfor loop, but nothing changes.

I'm using MATLAB R2016b on MACOS.

Any help is very appreciated. Thanks in advance

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Adam 2017-12-19

在 MATLAB Online 中打开

https://uk.mathworks.com/matlabcentral/answers/93826-are-matlab-user-defined-objects-supported-in-parfor-in-parallel-computing-toolbox-4-1-r2009a

may help. I don't know how your classes are defined so it is hard to say, but it appears you need to support the 0 input argument case in your constructor for use within a parfor loop.

Shouldn't this line:

q_0  = [ q1_0+vehicle.cog*(1-cos(q3_0)), q2_0+vehicle.cog*sin(q3_0), q3_0, q4_0, q5_0 ]';

refer to

vehicle(i)

instead?

Davide Fenucci 2017-12-19

编辑：Davide Fenucci 2017-12-19

According to this https://it.mathworks.com/matlabcentral/answers/339474-constructing-class-objects-within-a-parfor-loop everything should work fine, if objects are constructed outside the parfor loop. Should the 0 input argument constructor have to be supported in any case?

I have edited the post to fix the issue with the parameter vehicle.cog (typo after the simplification of the function)

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