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CGTTRF(l)			       )			     CGTTRF(l)

NAME
       CGTTRF  - compute an LU factorization of a complex tridiagonal matrix A
       using elimination with partial pivoting and row interchanges

SYNOPSIS
       SUBROUTINE CGTTRF( N, DL, D, DU, DU2, IPIV, INFO )

	   INTEGER	  INFO, N

	   INTEGER	  IPIV( * )

	   COMPLEX	  D( * ), DL( * ), DU( * ), DU2( * )

PURPOSE
       CGTTRF computes an LU factorization of a complex tridiagonal  matrix  A
       using elimination with partial pivoting and row interchanges.  The fac‐
       torization has the form
	  A = L * U
       where L is a product of permutation and unit lower bidiagonal  matrices
       and  U  is upper triangular with nonzeros in only the main diagonal and
       first two superdiagonals.

ARGUMENTS
       N       (input) INTEGER
	       The order of the matrix A.

       DL      (input/output) COMPLEX array, dimension (N-1)
	       On entry, DL must contain the (n-1) sub-diagonal elements of A.

	       On exit, DL is overwritten by the (n-1) 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 (N-1)
	       On entry, DU must contain the (n-1) super-diagonal elements  of
	       A.

	       On  exit,  DU is overwritten by the (n-1) elements of the first
	       super-diagonal of U.

       DU2     (output) COMPLEX array, dimension (N-2)
	       On exit, DU2 is overwritten by the (n-2) elements of the second
	       super-diagonal of U.

       IPIV    (output) INTEGER array, dimension (N)
	       The  pivot  indices;  for  1 <= i <= n, row i of the matrix was
	       interchanged with row IPIV(i).  IPIV(i) will always be either i
	       or  i+1;	 IPIV(i)  =  i	indicates  a  row  interchange was not
	       required.

       INFO    (output) INTEGER
	       = 0:  successful exit
	       < 0:  if INFO = -k, the k-th argument had an illegal value
	       > 0:  if INFO = k, U(k,k) 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.

LAPACK version 3.0		 15 June 2000			     CGTTRF(l)
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