Discrete-Time Systems: Examples Accumulator- Input-output relation can also be written in the form xl+>x C=0 y-1]∑x[(l,n≥0 C=0 The second form is used for a causal input sequence, in which case y[-l is called the initial condition Copyright C 2001, S K. MitraCopyright © 2001, S. K. Mitra 4 Discrete-Time Systems:Examples • Accumulator- Input-output relation can also be written in the form • The second form is used for a causal input sequence, in which case is called the initial condition =  +  = − =− n y n x x 0 1 [ ] [ ] [ ]     [ 1] [ ], 0 = − +  = n y x   y[−1] n  0