Parfor Closed loop variable

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Abhishek M 2014-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/115982-parfor-closed-loop-variable

编辑： Abhishek M 2014-2-21

Hi, Is it possible to have a closed loop model design which uses the initial value of inputs and later on the inputs are computed based on the output for further iterations, that is, the output is used again as the input for the next computation steps??

If yes, 1). Can it be implemented using parfor because my idea involves huge number of iterations consuming lot of time which I don't want to spend. 2). I tried using simin and simout for the input and output respectively. The model works in for loop but not in parfor:(. Can you suggest some other source and sink blocks for this implementation.

Thanks in Advance :)

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Matt J 2014-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/115982-parfor-closed-loop-variable#answer_124217

You can use the parfor to parallelize computation in individual iterations, possibly reducing time per iteration. However, you cannot parallelize across iterations. The iterations lack the parallel independence assumed by PARFOR.

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Abhishek M 2014-2-14

编辑：Matt J 2014-2-14

在 MATLAB Online 中打开

parfor_error.png

Hi Matt,

I am applying the parfor for my inner loop itself. i have attached a screen shot in this comment of my model "loopinloopmdl" which i am calling through my code which is represented as below. The variable 'x' is the input to the model which is loaded from the "WS_loop.mat" file which is also the output ofthe system which is used again as input for the 'i++' iteration

%%%%%%%%%%%%%%Code%%%%%%%%%
clear all
clc
model = 'loopinloopmdl';
% load_system(model)
tic;
for j=1:5    
      clear x;
      load('WS_loop.mat');
      load_system(model)
      parfor i=1:10
          simout= sim(model);          
      end
    %  x = get(si,'xout');
      plot(x,'--xk')
          hold all
      c=x;    
  end
  toc;
  %%%%%%%%%%%%%%Code%%%%%%%%%

The above code is running fine with regular "for loop". But when i change the loop of 'i' iteration to parfor i get the following errors.

%%%%%%%%%%%%%%Error%%%%%%%%%%%%%%
Caused by:
      Error using
      parallel_function>make_general_channel/channel_general
      (line 906)
      Error evaluating parameter 'VariableName' in
      'loopinloopmdl/From Workspace'
          Error using
          parallel_function>make_general_channel/channel_general
          (line 906)
          Undefined function or variable 'x'. 
%%%%%%%%%%%%%%Error%%%%%%%%%%%%%%

Could you please help me out with this..

Thanks in advance.

Matt J 2014-2-19

在 MATLAB Online 中打开

As far as I can see, you aren't currently doing anything to save the results of the different outer loop iterations, j, even in your regular for-loop. If x is supposed to be the output, you could do, e.g.,

   parfor j=1:5
     ...
    X{j}=x;
   end

Incidentally, the code you show is using the same input file 'WS_loop' for every outer iteration, j. Since the input is always the same, the results of all those iterations will be identical, meaning you're just doing unnecessary repeat work.

Abhishek M 2014-2-20

编辑：Abhishek M 2014-2-21

Yeah Matt, i know i am repeating the same thing again n again but as i said this is just a demo model. The actual implementation model involves random numbers and huge logical calculations whose output varies with each simulation for the same inputs.

Anyways, thanx a lot for your help and suggestions on this.

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