sys variables for control theory

[Doug Stewart]

These thoughts are for those that use octive for control theory and design.
I was trying to model a PID controller and use it in a closed loop 
negative feed back loop. The PID numerator is a quadratic equation and 
the denominator is first order. Thus the numerator is of higher order 
than the denominator. Octave's tf2sys.m does not like this but Matlab's
tf.m thinks it is OK. I understand that you can't do a step or bode etc.
on this PID, but I should be able to use it in sysmult.m to form up Gs.
Then use this with feedback to get the closed loop system, and then use 
step etc.

I think we should take the checking out of tf2sys and let it make any 
shape of transfer function.

Any comments?????

I will do the work if there is no real objections.

Doug Stewart



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