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StateSpaceModel: new bug in 10.2

Posted 9 years ago

I don't know if this is a bug, or if just something changed I can't figure out.

Take the following examples:

sysEq = y'''[t] == -1/T2^2 y'[t] - T1/T2^2 y''[t] + Ki/T2^2 u[t];
sysEq1 = y[t] == Kp u[t];
sysEq2 = y'[t] + (T1 + T2) y''[t] + T1 T2 y'''[t] == Ki u[t];
sysEq3 = Tn y'[t] == Kp u[t] + Kp Tn u'[t];
sysEq4 = y'[t] + T1 y''[t] + T2 y'''[t] == Kp u[t];
sysEq5 = Tn y'[t] + T1 Tn y''[t] + T2^2 Tn y'''[t] == 
   Kp u[t] + Kp Tn u'[t];
sysEq6 = Tn y'[t] + T1 Tn y''[t] + T2^2 Tn y'''[t] == 
   Kp u[t - Tt] + Kp Tn u'[t - Tt];
sysEq7 = y'[
     t] + (T1 + T2 + T3) y''[t] + (T1 T2 + T1 T3 + T2 T3) y'''[t] + 
    T1 T2 T3 y''''[t] == Ki u[t - Tt - Tt2] + Kp u'[t - Tt - Tt2];
allExamples = {sysEq, sysEq1, sysEq2, sysEq3, sysEq4, sysEq5, sysEq6, 
   sysEq7};

In v10.0 all examples work:

FullSimplify@TransferFunctionModel[
    StateSpaceModel[#, {{y[t], 0}}, {{u[t], 0}}, {y[t]}, t]
    ] & /@ allExamples

But not in v10.2, example 6 and 7 won't give a proper result.

Can somone confirm this, or show me where StateSpaceModel has changed so it doesn't work for this examples?

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POSTED BY: Fabian Wiek

This is a bug, unfortunately. But it's been fixed in the development version so the next version of Mathematica will give the correct answer.

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