There are two errors in my code. Can someone know how to edit it to maker it run? Thank you!

Here is the function:

function [L,U] = eluinv(A)
[~,n]=size(A);
[L,U] = lu(A);
format compact
if closetozeroroundoff(A,7) == closetozeroroundoff(L*U,7)
    disp('Yes, I have got LU factorization')
end
if closetozeroroundoff(rref(U),7) == closetozeroroundoff(rref(A),7)
    disp('U is an echelon form of A')
else
    disp('Something is wrong')
end
if rank(A) ~= min(size(A))
    sprintf('A is not invertible')
    invA=[];
    return
else
    leye = [L eye(size(L,1))];
    ueye = [U eye(size(U,1))];
    invLech = rref(leye);
    invUech = rref(ueye);
    invL = invLech(:,(n+1):size(invLech,2));
    invU = invUech(:,(n+1):size(invUech,2));
    invA = invU*invL;
    if isequal(closetozeroroundoff(invA-inv(A)),zeros(size(A)))
        disp('Yes, LU factorization works for calculating the inverses')
    else
        disp('LU factorization does not work for me?!')
    end
end

Answer 1

[Cris LaPierre]

The error message appears to show the reason for the error. Your matrix A must be square (3x3 or 4x4) in order to use inv.

if isequal(closetozeroroundoff(invA-inv(A)),zeros(size(A)))
                                    ^^^^^^ % Error is here

[Tianlan Yang]

But I use these codes to take such situation:

if rank(A) ~= min(size(A))

sprintf('A is not invertible')

Do you know how to print out this message when the matrix is not square? Thank you.

[Cris LaPierre]

Your criteria do not check if the matrix is square. Perhaps you want this instead?

rank(A) ~= max(size(A))

[Tianlan Yang]

That works. Thanks