mean(aR2) is a scalar value, why you want to store it into a vector?
Are you looking for saving values in a loop into a array? Then consider below example.
n = 30 ;
A = rand(1,n) ;
iwant = zeros(1,n) ;
for i = 1:n
iwant(i) = rand*A(i)
end
The above can alos be achieved without loop.
