How to sum the product between a matrix and 2 vectors

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Sara Crosetto
Sara Crosetto 2020-12-17
回答： Karan Singh 2025-1-31
I need to solve a system of differential equation written as:
For each equation I should solve a summation like:
where K_Br is a matrix previously calculated and n is a vector as the solution of the differential equation system.
For example, for i=3:
I wrote the system of differential equation as:
function ndot = System_ni (t,n)
ndot = zeros(M,1);
ndot(1) = -n(1)*sum(K_Br(1,1:M)*n(1:M));
for i = 2:M
ndot(i) = 1/2*sum(K_Br(1:i-1,i-1:1)*n(i-1:1)*n(1:i-1))-n(i)*sum(K_Br(i,1:M)*n(1:M));
end
end
but summation seems not to work.
Thank you in advance for any help.
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Sara Crosetto
Sara Crosetto 2020-12-18
I reported the initial equation wrong.
Actually, the equation is:
VBBV
VBBV 2024-4-8
@Sara Crosetto the terms in equation shown are dependent on another implicit summing variable i
You need two for loops instead of one for such summation to work.

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回答（1 个）

Karan Singh
Karan Singh 2025-1-31
Hi Sara,
I think you are not performing the element-wise operation correctly. How about using " .* " instead of " * " for element-wise multiplication? This MATLAB answer might be of help:What does mean .* and ' ? - MATLAB Answers - MATLAB Central for you to carry out the process.

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