SGTTRF(l)		LAPACK routine (version	1.1)		    SGTTRF(l)

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

SYNOPSIS

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

      INTEGER	     INFO, N

      INTEGER	     IPIV( * )

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

PURPOSE
  SGTTRF computes an LU	factorization of a real	tridiagonal matrix A using
  elimination with partial pivoting and	row interchanges.

  The factorization 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) REAL array, dimension (N-1)
	  On entry, DL must contain the	(n-1) subdiagonal 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) REAL 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) REAL array, dimension (N-1)
	  On entry, DU must contain the	(n-1) superdiagonal elements of	A.
	  On exit, DU is overwritten by	the (n-1) elements of the first
	  superdiagonal	of U.

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

  IPIV	  (output) INTEGER array, dimension (N)
	  The pivot indices; for 1 <= i	<= n, row i of the matrix was inter-
	  changed 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	= -i, the i-th 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.