What is wrong with my code ? It works well six years ago.

It is the case of a singular matrix.

I review the following exercise: Compute the LU factorization of the matrix

A=[1 2 -1 3 2;2 4 -2 5 1;-1 -2 1 -3 -4;3 6 2 10 7; 1 2 4 0 4].

The used code is:

using LinearAlgebra

A=[1 2 -1 3 2;2 4 -2 5 1;-1 -2 1 -3 -4;3 6 2 10 7; 1 2 4 0 4].

(L,U,p)=lu(A)

Error message: Error: SingularException

and

(L,U,p)=lu(A,check=false)

Error message: Failed factorization of type LU(Float64, Matrix(Float64))

When the matrix is not singular then the lu factorizarion works

without problem.