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>> rng('default');
>> A = randi(3, 2, 3); B = randi(3, 3, 2);
>> A*B
ans =
11 16
12 15
>> C = zeros(size(A, 1), size(B, 2));
>> for j = 1:size(A, 2),
C = C + A(:, j) * B(j, :);
end
>> C
C =
11 16
12 15

矩阵的迹等于其对角元素之和;
function t = trace(A)
if ~ismatrix(A) || size(A,1)~=size(A,2)
error(message('MATLAB:trace:square'));
end
t = full(sum(diag(A)));
基本性质:
>> A = magic(3);
>> norm(A, 'fro')^2
ans =
285.0000
>> trace(A'*A)
ans =
285
>> trace(A*A')
ans =
285
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