# Error "Matrix dimensions must agree" in the line "T = norm(rref(Y)- rref(U)) < tol;" I used "A=[1 1 4;0 -4 0;-5 -1 -8; 2 3 -1] [L,U] = eluinv(A);" in my livescript. Thank you so much!

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Tianlan Yang on 18 Mar 2021
Commented: Tianlan Yang on 18 Mar 2021
Here is the function.m:
function [L,U] = eluinv(A)
[m,n] = size(A);
[L,U] = lu(A);
B = L*U;
C = closetozeroroundoff(B,7);
q = closetozeroroundoff(A,7);
if q == C
disp('Yes, I have got LU factorization');
end
Y = closetozeroroundoff(A,7);
tol = 1e-6;
T = norm(rref(Y)- rref(U)) < tol;
if T
disp('U is an echelon form of A');
else
disp('Something is wrong')
end
if rank(A) ~= n
sprintf('A is not invertible');
invA = [];
return
else
invL = eye(n)/rref(L);
invU = eye(n)/rref(U);
invA = invU * invL;
end
P = inv(A);
J = closetozeroroundoff(P,7);
Q = closetozeroroundoff(invA,7);
if J == Q
disp('Yes, LU factorization works for calculating the inverses');
else
disp('LU factorization doesnt work for me');
end
Tianlan Yang on 18 Mar 2021
Edited: Tianlan Yang on 18 Mar 2021
Could you please show how to make it work? Because I try 3*4 matrix, it works, but when I try 4*3 matrix, it shows error. Thank you!

KSSV on 18 Mar 2021
Replace the line:
T = norm(rref(Y)- rref(U)) < tol;
with
T = (norm(rref(Y))- norm(rref(U))) < tol;
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Tianlan Yang on 18 Mar 2021
That works. Thank you.