Prove that the matrix A = [0 1 1 0] has no LU factorization, i. e., no lower triangular matrix L and upper triangular matrix U exist, such that A = LU. Hint: Assume that there is an LU decomposition [l11 0 l21 l22] [u11 u12 0 u22] = [0 1 1 0] and arrive at a contradiction!