How to reinitialize a continuous variable which isn't a state

[modelica-trac-importer]

Reported by AHaumer on 7 May 2008 11:01 UTC
The Modelica specification doesn't allow to reinit a continuous variable which isn't a state;
but how should I get the peak value of a signal with respect to predefined periods:

block PosPeak "Positive peak during one period"
  extends Modelica.Blocks.Interfaces.SISO;
  parameter Modelica.SIunits.Frequency f=1 "Basic signal frequency";
protected
  Real x;
equation
  x=max(u,x);
  when sample(0, 1/f) then
    y=x;
    reinit(x,u); // not standard compliant!
  end when;
end PosPeak;

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Migrated-From: https://trac.modelica.org/Modelica/ticket/74

[modelica-trac-importer]

Modified by dietmarw on 7 May 2008 16:47 UTC

[modelica-trac-importer]

Comment by sebastien on 30 Jun 2008 09:54 UTC
Replying to [ticket:74 AHaumer]:

The Modelica specification doesn't allow to reinit a continuous variable which isn't a state;
but how should I get the peak value of a signal with respect to predefined periods:

block PosPeak "Positive peak during one period"
  extends Modelica.Blocks.Interfaces.SISO;
  parameter Modelica.SIunits.Frequency f=1 "Basic signal frequency";
protected
  Real x;
equation
  x=max(u,x);
  when sample(0, 1/f) then
    y=x;
    reinit(x,u); // not standard compliant!
  end when;
end PosPeak;

This model is not correct. "x=max(u, x)" does not constraint x when x >= u. IMO a correct version is:

block PosPeak "Positive peak during one period"
extends Modelica.Blocks.Interfaces.SISO;
parameter Modelica.SIunits.Frequency f=1 "Basic signal frequency";
protected
Real x;
equation
der(x) = if u >= x then der(u) else 0;
when sample(0, 1 / f) then
y = x;
reinit(x, u);
end when;
end PosPeak;

so that x is now a real state.

[modelica-trac-importer]

Comment by HansOlsson on 8 Sep 2008 19:35 UTC
Discussed in language grp of 58th design meeting:

Conclusion seems to be:
Peak-detection (and impulses in general) are interesting, but the functionality in this ticket does not seem directly useful.