matlab dymola connection fails after a while

Question

I have data of an experiment in a .mat file and a model written in dymola. I use the dymolaM.m file to send commands from matlab to dymola. In that way I can use matlab to optimize a parameter of my model. Matlab reads in the data from the .mat file, initialises dymola in a correct way, lets dymola simulate the model, reads in the output of dymola and compares it with the experimental data.

This all works fine for a wile, but if I repeat the matlab dymola connection too much I always get the following error:

    ??? Error using ==> ddeexec
    The first argument 'channel' is not valid.

    Error in ==> dymolaM at 59
    status = ddeexec(DymolaChannel, deblank(command(i,:)), '', timeout);

I tried repeating exactly the same command 200 times. I always got the error at iteration 26.

What should I do? This is the code of the dymolaM.m file

    function res=dymolaM(command, value)
    % Executes a command optionally followed by a value in Dymola.
    % Dymola is started if not already running.

    % Version 1.0, 1997-11-14
    % Version 1.1, 1999-06-12

    %    Copyright (C) 1997-2001 Dynasim AB.
    %    All rights reserved.

      DymolaChannel = ddeinit('dymola', ' ');
      if DymolaChannel == 0,
         pause(1);
         DymolaChannel = ddeinit('dymola', ' ');
         if DymolaChannel == 0,
           dymola    = getenv('DYMOLA');
           v=version;
            if (isempty(dymola) & v(1,1)>='5') 
                if v(1,1)>='7'
         [st,I]=dbstack('-completenames');
       else
         [st,I]=dbstack;
       end
       if v(1,1)>='7'
          currentfile=st(I).file;
       else
         currentfile=st(I).name;
       end
             I=find(currentfile=='\' | currentfile=='/');
             currentfile=currentfile(1:(max([1,I(1:end-1)])-1));
             dymola=currentfile;
           end
           if ~isempty(dymola)
              dymola=[dymola,'\bin\'];
           end
           disp('Starting Dymola - Wait');
           fquote    = '';
           if strcmp(computer, 'PCWIN') | strcmp(computer, 'PCWIN64')
            fquote = '"';
           end;
           dos([fquote,dymola,'Dymola',fquote,' &']);
           pause(10);
           DymolaChannel = ddeinit('dymola', ' ');
           disp('Dymola started');
        else
           disp('Worked around problem communicating with Dymola');
        end
      end
      if nargout>0
         res=zeros(size(command,1),1);
      end

      if DymolaChannel == 0,
         disp('Error starting Dymola');
      elseif nargin > 0,
         for i=1:size(command,1)
              timeout=4000*1000; % Can always kill dymola
              if nargin == 1, 
                 status = ddeexec(DymolaChannel, deblank(command(i,:)), '', timeout);
              elseif nargin == 2,
                 status = ddeexec(DymolaChannel, [deblank(command(i,:)), num2str(value(i))], '', timeout);
              end
              if nargout==0 
                 if status == 0,
                    error('Invalid Dymola command.');
                 end
              else
                 res(i)=status;
              end;
            end
            ddeterm(DymolaChannel);
      end

Answer 1

OK, this problem is four years old, but I just spent the last two weeks usings unsatifactory workarounds before finally getting to this solution.

I solved the problem with the following tactic:

I overloaded the function dymolaM.m with my own modified version. I commented out the command:

DymolaChannel = ddeinit('dymola', ' ');

and replaced it with:

% DymolaChannel = ddeinit('dymola', ' ');
DymolaChannel = get_dymola_channel();

I defined the function get_dymola_channel(); as follows:

function DymolaChannel = get_dymola_channel()
    persistent dymola_channel_persistent
    if isempty(dymola_channel_persistent)
        dymola_channel_persistent = ddeinit('dymola', ' ');
    end
    DymolaChannel = dymola_channel_persistent;
end

This means the function ddeinit (which can only create a limited number of channels) is only called once.