Sigma notation with matrices
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I am trying to model a differential equation including 
, where C is a 4 by 4 matrix, i are rows, and j are vectors. The sigma notation is crucial towards using the interaction coefficient 
with the proper elements in the matrix. I don't at all know what I'm doing, and have been using symsum so far but have gotten absolutely nowhere. How do I code this without getting "Subscript indices must either be real positive integers or logicals errors"?
, where C is a 4 by 4 matrix, i are rows, and j are vectors. The sigma notation is crucial towards using the interaction coefficient with the proper elements in the matrix. I don't at all know what I'm doing, and have been using symsum so far but have gotten absolutely nowhere. How do I code this without getting "Subscript indices must either be real positive integers or logicals errors"?采纳的回答
Star Strider
2019-7-13
Taking a wild guess:
x = rand(1,4); % Create Vector
C = rand(4); % Create Matrix
for i = 1:4
for j = 1:4
E(i,j) = C(i,j)*x(i)*x(j); % Multiplications
end
end
S = sum(E(:)); % Summation
There are likely more efficient ways to do this, however I am choosing to keep this as transparent as possible. Note that symsum is not intended to do this type of summation.
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