On Thu, Mar 25, 2010 at 9:48 PM, Axax
<address@hidden> wrote:
Hi,
I'm trying to defina a system with the function tf() but I got this
error:
octave:49> tf([1 0.8],[1])
error: # of poles (0) < # of zeros (1)
I can't understand why I can't define a system with a zero only!
There are some reasons for that?
Thanks for the help
Axel
Yes there is.
Try doing the inverse Laplace transform on s
inverse of (1/s) is a step function
inverse of (1) is an impulse function
inverse of (s) is ??? Well it is the derivative of the impulse function ---- which is a positive going impulse and a negative going impulse at the same time.
Have fun doing the inverse of s^2 :-)
So Octave and math in general needs the numerator to be of the same or less order of polynomials.
If you are working in control theory and you say "yes but I can build the circuit and it works -- so why can't we simulate the circuit that I built" --- then the answer is that there are some high frequency poles on your opamp that you are ignoring. So just add some high frequency poles and keep your DC gain the same. and it will work.
1000
--------
s + 1000
My students run into this every year :-)
Doug Stewart
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