What's the pattern? I can't quite figure it out. I know every other one is 4, but what about the 1 and the 2? It's not just alternating because there are 2 2's in a row near the end. Is it 4,2 except the very first and very last are 1? Or are there 1's in the middle somewhere?
Anyway, you know the rule (whatever it is), so just use repmat
y = repmat(.......
Then use
y(2:2:end) = 4;
Or maybe try this:
y = ones(1,2000);
y(2:2:end-1) = 2;
y(3:2:end-1) = 4
