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.