Some bold guesses of what you want to achieve:
aa = [9 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9];
a = aa;
a(a >= 5) = 0
a = aa;
a(~ismember(a, 1:4)) = 0
a = aa;
a(ismember(a, 5:9)) = 0
a = aa;
a([1:5, end-4:end]) = 0
a = aa;
n = numel(a);
a(abs((1:n) - (n + 1)/2) >= 5) = 0
There is an infinite number of methods to produce the wanted output based on the given input. The current explanations are not enough to find the general solution.
