Problems with the number of iterations

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Problems with the number of iterations

Problems with the number of iterations

Mar-18-14 18:42:28

Hi Guys,

I am trying to run Exercise 3 in Chapter 9 of Dr.Modelica, Algorithms. The algorithm is meant to find the sum of 1*(1*1)-1/(2*2)+1/(3*3)+1/(4*4)-1/(5*5)+1/(6*6).....
The code is implemented as below:

class SumCalculation
constant Real e = 0.000001;
Real sum(start = 0);
Real next(start = 1.0);
Integer k(start = 1);
Integer posneg(start = 1);
algorithm
while noEvent(abs(next)) >= e loop
sum := sum + next;
k := k + 1;
posneg := - posneg;
next := posneg/(k*k);
end while;
end SumCalculation;

When I try to simulate the above I get:

record SimulationResult
resultFile = "",
messages = "Simulation execution failed for model: SumCalculation
assert | debug | ERROR: Too many event iterations. System is inconsistent. Simulation terminate.
"
end SimulationResult;

I do not know why this code is giving me this error. I tried to decrease the number of iterations but I have the same problem. Could you please advice me where the problem might be?

Thank in advance

Malen: 25 Posts; Thank you [ 0 ]

#4319 Permalink

Re: Problems with the number of iterations

Mar-19-14 18:21:10

Hi,

as far as I see the solution in DrModelica there is wrong, since
the variables k is discrete and next is continuous. That means
they are treated different when the algorithm is initialized
(see Modelica Specification: 11.1.2).

So these both variables should treated the same.
I suggest to change all variables to the same variability:

Code:


class SumCalculation

  constant Real e = 0.000001;

  Real sum(start = 0);

  Real next(start = 1.0);

  Real k(start = 1);

  Real posneg(start = 1);

algorithm

  while noEvent(abs(next) >= e) loop

    sum := sum + next;   

    k := k + 1;           

    posneg := - posneg;

    next := posneg/(k*k);

end while;

end SumCalculation;

Also the noEvent() operator should applied
to the whole relation, since abs(v) is expanded to
noEvent(if v >= 0 then v else –v).
But actually the noEvent is not needed there at all, but
that a bug(see ticket #2618) in OpenModelica.