Consider a filter described by the following recursive difference equation:

*y*(*k*) = *x*(*k*) -
0.2*y*(*k*-1) - 0.8*y*(*k*-2)

You can easily specify and implement this filter in time
domain using unitDelay blocks. The filter input is *x*(*k*) and the
filter output is *y*(*k*). The intermediate states are
*y*(*k*-1) and *y*(*k*-2). The filter can be implemented
as:

The Time Between Pulses parameter for the pulseTrain block
must be greater than or equal to the simulation time step. An arbitrary value of
1 is assigned to input *x*.