SYNOPSIS
 SUBROUTINE SDTTRF(
 N, DL, D, DU, INFO )
 INTEGER INFO, N
 REAL D( * ), DL( * ), DU( * )
PURPOSE
SDTTRF computes an LU factorization of a complex tridiagonal matrix A using elimination without partial pivoting.
The factorization has the form
A = L * U
where L is a product of unit lower bidiagonal
matrices and U is upper triangular with nonzeros in only the main
diagonal and first superdiagonal.
ARGUMENTS
 N (input) INTEGER
 The order of the matrix A. N >= 0.
 DL (input/output) COMPLEX array, dimension (N1)
 On entry, DL must contain the (n1) subdiagonal elements of A. On exit, DL is overwritten by the (n1) multipliers that define the matrix L from the LU factorization of A.
 D (input/output) COMPLEX array, dimension (N)
 On entry, D must contain the diagonal elements of A. On exit, D is overwritten by the n diagonal elements of the upper triangular matrix U from the LU factorization of A.
 DU (input/output) COMPLEX array, dimension (N1)
 On entry, DU must contain the (n1) superdiagonal elements of A. On exit, DU is overwritten by the (n1) elements of the first superdiagonal of U.
 INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
> 0: if INFO = i, U(i,i) is exactly zero. The factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations.