MATLAB: How to calculat the sequence

Question

Answer 1

u = rand(1,100) ; % data for demo 
k = 20 ; 
thesum = 0 ;
for j = 1:k-1
    thesum = thesum+sqrt(k-j)*u(j) ; 
end

You can achieve the same without loop using:

j = 1:k-1 ; 
iwant = sum(sqrt(k-j).*u(j))