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RedHat 9 (Linux i386) - man page for sgttrf (redhat section l)

SGTTRF(l)					)					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 tri-
       angular 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) 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) 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) super-diagonal elements of A.

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

       DU2     (output) REAL 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 				SGTTRF(l)


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