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modelicadymola

An initialization warning in Dymola

In my model, I got confused that why the initial conditions are NOT fully specified.

Here are the code and screenshot:

model WithAlgebraicLoop_Right
  extends Modelica.Icons.Example;
  Real x;
  Real y(start=1, fixed=true);
  Boolean cond;
equation 
  cond = x > 0.5;
  when pre(cond) then
    y = 1*time;
  end when;
  x = sin(y*10*time);
end WithAlgebraicLoop_Right;

enter image description here

I think that during the initialization, x could be calculated from y, so cond could be calculated from x, so why doesn't Dymola do as I think?

Solution

  • Sure, discrete-time variable cond can be calucated according to the given equations. However, its pre-value for the event iteration at initialization is not known and must be set, either by setting a fixed start value or by an initial equation, whatever you prefer.

    model WithAlgebraicLoop_Right1
  Real x;
  Real y(start=1, fixed=true);
  Boolean cond(start=false, fixed=true);
equation 
  cond = x > 0.5;
  when pre(cond) then
    y = 1*time;
  end when;
  x = sin(y*10*time);
end WithAlgebraicLoop_Right1;

    or

    model WithAlgebraicLoop_Right2
  Real x;
  Real y(start=1, fixed=true);
  Boolean cond;
initial equation
  pre(cond) = false;
equation 
  cond = x > 0.5;
  when pre(cond) then
    y = 1*time;
  end when;
  x = sin(y*10*time);
end WithAlgebraicLoop_Right2;