How can calculate this formula with matlab?

I have the vectors w(1,n) and σ(n,1). How can calculate this formula?

Answer 1

[Thorsten]

You can pull the w_i and sigma_i outside of the sum_j, because the don't depend on j. And you can compute the sum_j nicely as a matrix multiplication of row vector w and column vector sigma.

w = rand(1,10); % sample values for w and s
s = rand(10, 1);

N = numel(w);
y = 0; 
for i=1:N-1
  y = y + s(i)*w(i)* w(i+1:end)*s(i+1:end);
end
y = 2*y;

[fede]

give me Error using * Inner matrix dimensions must agree.

[Torsten]

Note that "w" must be a row vector whereas "s" must be a column vector if you want to use Thorsten's code.

Best wishes

Torsten.

Answer 2

[Torsten]

sum_total=0.0;
for i=1:(N-1)
  sum_j=0.0;
  for j=(i+1):N
    sum_j = sum_j + w(j)*sigma(j);
  end 
  sum_total = sum_total + w(i)*sigma(i)*sum_j;
end 
sum_total = 2.0*sum_total;

Best wishes

Torsten.