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In the LU decomposition method, I used a 4*5 matrix. However, L and U should originally come out as 4*5 matrices, but both come out only 4*4 matrices. What is the cause?

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SUNGJIN KIM
SUNGJIN KIM 2020-11-27
编辑： SUNGJIN KIM 2020-11-27
function [L,U] = LU(A)
A = [4 -2 -3 6 12;-6 7 6.5 -6.5 -6.5;1 7.5 6.25 5.5 16;-12 22 15.5 -1 17];
[m,n] = size(A);
for i = 1:m
L(i,1) = A(i,1);
U(i,i) = 1;
end
for j = 2:m
U(1,j)= A(1,j)/L(1,1);
end
for i = 2:m
for j = 2:i
L(i,j)=A(i,j)-L(i,1:j-1)*U(1:j-1,j);
end
for j = i+1:m
U(i,j)=(A(i,j)-L(i,1:i-1)*U(1:i-1,j))/L(i,i);
end
end
L
U
----------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------
so. The answer comes out like this, but what is the problem here >>??? And I only need to show L U, but I don’t know if ans comes............
L =
4.0000 0 0 0
-6.0000 4.0000 0 0
1.0000 8.0000 3.0000 0
-12.0000 16.0000 -1.5000 6.5000
U =
1.0000 -0.5000 -0.7500 1.5000
0 1.0000 0.5000 0.6250
0 0 1.0000 -0.3333
0 0 0 1.0000
ans =
4.0000 0 0 0
-6.0000 4.0000 0 0
1.0000 8.0000 3.0000 0
-12.0000 16.0000 -1.5000 6.5000

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