Identify possible feedback data
[fbck,fbck0,nudir] = feedback(Data)
Data is an iddata set
with Ny outputs and Nu inputs.
fbck is an Ny-by-Nu matrix
indicating the feedback. The ky,ku entry is a
measure of feedback from output ky to input ku.
The value is a probability P in percent. Its
interpretation is that if the hypothesis that there is no feedback
from output ky to input ku were
tested at the level P, it would have been rejected.
An intuitive but technically incorrect way of thinking about this
is to see P as “the probability of feedback.”
Often only values above 90% are taken as indications of feedback.
When fbck is calculated, direct dependence at lag
zero between u(t) and y(t)
is not regarded as a feedback effect.
fbck0: Same as fbck, but
direct dependence at lag 0 between u(t)
and y(t) is viewed as feedback
effect.
nudir: A vector containing those input numbers
that appear to have a direct effect on some outputs, that is, no delay
from input to output.