I've been trying to understand how the tapped delay line (TPL) work  with a linear layer in MATLAB, but i have been unsuccessful. MATLAB mention an initial input delay state called "Pi" but I can not understand the influences or effects of "Pi" in time series prediction. I would appreciate if you could instruct me with some basic example, or a detailed explanation of how to work with the instruction new line, due the information I've found is similar to that provided by MATLAB. Thank you.