DGTTRF(l)								 )								 DGTTRF(l)

NAME

       DGTTRF - compute an LU factorization of a real tridiagonal matrix A using elimination with partial pivoting and row interchanges

SYNOPSIS

       SUBROUTINE DGTTRF( N, DL, D, DU, DU2, IPIV, INFO )

	   INTEGER	  INFO, N

	   INTEGER	  IPIV( * )

	   DOUBLE	  PRECISION D( * ), DL( * ), DU( * ), DU2( * )

PURPOSE

       DGTTRF  computes an LU factorization of a real 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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) DOUBLE PRECISION 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 							 DGTTRF(l)