Yes, you get new u and v vectors every time - is that what you mean by successive? By the way you should do it this way:
t = [0,4,8,12,16,20]
y = [0.7,0.9,0.9,0.7,0.3,0]
for k = 1 : 3 : length(t)-2
% Get a new u and v for this iteration:
u = t(k : k+2);
v = y(k : k+2);
% Now do something with u and v....
end
