Summation using for-loop

Hi Everyone, I want to ask a question about summation using for-loops. My question is similar to this previous questions. http://www.mathworks.com/matlabcentral/answers/23155-summation-with-looping

However, there are some differences in my case. I am struggling how to present this equation on Matlab. (attached photo)

Here is my code:

for M=1:a;
    for R=1:a;
      [M]=(K1*(conj(K2)))\(P^2) ; 
      [R]=(K1*(conj(K2)))\(P^2);
      [B]= atan2(imag(M) ,real(R ));

     sum(B);

      end
  end

This is one part of an function and Matlab debug gave me an error "Not enough input arguments." at the line "for M=1:a". Is the matrix unmatched? Besides, is the for-loop correct and enough to represent the equation? How should I change my code, please?

Thank you!!