Computing determinant of matrix A using LU factorization

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Emily Gallagher
Emily Gallagher 2019-10-8
评论： the cyclist 2019-10-8
I must compute the determinant of an nxn matrix A using LU factorization. I have already calculated L and U in a different 'lufact' function. For some reason though, my funcion for computing the determinant of A, which is just equal to the product of the diagonal entries of matrix U is not working.
seed = 7;
rng(seed)
A = randn(n,n);
[L,U] = lufact(A);
function f = determ(A)
%Computing determinant of A
f = prod(diag(U));
end
  1 个评论
the cyclist
the cyclist 2019-10-8
One weirdness here. If your function definition is really
function f = determ(A)
%Computing determinant of A
f = prod(diag(U));
end
then that is going to throw an error, because you don't pass in U. So, maybe you are not really calculating with the inputs you expect?

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回答（1 个）

the cyclist
the cyclist 2019-10-8
编辑：the cyclist 2019-10-8
If I use the lu function from MATLAB (instead of your lufact function), I get the expected result. So, I'd double-check your LU factorization code.
seed = 7;
n = 5;
rng(seed)
A = randn(n,n);
[L,U] = lu(A);
f = prod(diag(U))
d = det(A)
f =
-8.0745
d =
-8.0745

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