Z-transform - Wikipedia
https://en.wikipedia.org/wiki/Z-transformThe region of convergence (ROC) is the set of points in the complex plane for which the Z-transform summation converges. Let x[n] = (0.5) . Expanding x[n] on the interval (−∞, ∞) it becomes Looking at the sum Therefore, there are no values of z that satisfy this condition.
Z-transform - Wikipedia
en.wikipedia.org › wiki › Z-transformIn signal processing, this definition can be used to evaluate the Z-transform of the unit impulse response of a discrete-time causal system.. An important example of the unilateral Z-transform is the probability-generating function, where the component [] is the probability that a discrete random variable takes the value , and the function () is usually written as () in terms of =.