In: Advanced Math
LU Decomposition
(i). Prove that for n equal to 2 or 3 there is a non-singular square (n by n) matrix which has no LU decomposition with L unit lower triangular and U upper triangular. (In fact, this is true for any integer ≥ 2.)
(ii). We will see that all non-singular square matrices do have an LUP decomposition (some time soon in class). Here P is a permutation matrix, also defined in Appendix D and used in Chapter 28.
Show that the inverse of a permutation matrix P is also a permutation matrix. (You can do this by explicitly defining what P −1 when P is given.)