matlab+echo+delay
q(s) refers to the actual echo(in a communication system echo refers to a delayed version of input i.e if the input starts at t=0,then echo would get added to it after sometime say 4s.)
the above LOC delays the i/p(dependin on echo delay)to generate an echo.
now lets assume samples=10 and echo delay=4,echo_amp=0.5, then echo must be produced after 4 samples of input(with half the mag of input)
if i/p has the value say 6 2 4 5 6 9 7 8 2 3 .then echo q(s)=0.5 *( 0 0 0 0 6 2 4 5 6 9).