]???y(x)=0 [1132] This result is based on extending the result derived above for digital signals to infinite sums and using a limiting argument to integrals. [1133] Complex Digital Signals [1134] If the data are a elements of a complex discrete function ???i where ???i corresponds to a set of complex numbers ???1, ???2, ???3, . . . , then we use the mean square error defined by e = ??? i ??? ??? f