Nyquist frequency signal, whereas "Nyquist frequency" is a property of a discrete-time system. When the function domain is time, sample rates are usually expressed in samples per second, and the unit of Nyquist frequency is cycles per second (hertz). When the function domain is distance, as in an image sampling system, the sample rate might be dots per inch and the corresponding Nyquist frequency would be in cycles/inch. Referring again to Figure 1, undersampling of the sinusoid at 0.6 f is what allows there to be a lower-frequency "alias", which is a different function that produces the same set of samples. That
Shannon capacity of a graph "α"("G"). The effective number of signals transmitted per unit time step is the "k"th root of this number, "α"("G"). Using these concepts, the Shannon capacity may be defined as the limit (as "k" becomes arbitrarily large) of the effective number of signals per time step of arbitrarily long confusion-free codes. The computational complexity of the Shannon capacity is unknown, and even the value of the Shannon capacity for certain small graphs such as "C" (a cycle graph of seven vertices) remains unknown. A natural approach to this problem would be to compute a finite number of powers of the given