Question: why Maple control system do not allow one to create state space directly from differential eq?

If the differential equation has second derivative in the RHS (i.e. in the input), then `StateSpace` gives an error.

I might not be entering it correctly? But if I first create a `TransferFunction` from the ODE, then it works.

Why?

Here is the code:

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restart;
alias(DS=DynamicSystems):
ode2:=diff(y(t),t$2)+2*diff(y(t),t)+3*y(t)=diff(u(t),t)+u(t);
sys:=DS:-StateSpace(ode2,'outputvariable'=[y(t)],'inputvariable'=[u(t)]):
-------------------------
Error, (in DynamicSystems:-StateSpace) unable to convert the differential equation system:  invalid form of derivative in differential equation


But now if I do this, it works:

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restart;
alias(DS=DynamicSystems):
ode2:=diff(y(t),t$2)+2*diff(y(t),t)+3*y(t)=diff(u(t),t)+u(t);
sys:=DS:-TransferFunction(ode2,'outputvariable'=[y(t)],'inputvariable'=[u(t)]):
sys:=DS:-StateSpace(sys);
-----------------------------------------------

Maple 18.01 on windows 7.