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LAPACK version 3.0
dpttrf(3)

PURPOSE
  DPTTRF - compute the L*D*L' factorization of a real symmetric positive
  definite tridiagonal matrix A

SYNTAX
  SUBROUTINE DPTTRF( N, D, E, INFO )

      INTEGER	     INFO, N

      DOUBLE	     PRECISION D( * ), E( * )

DESCRIPTION
  DPTTRF computes the L*D*L' factorization of a real symmetric positive
  definite tridiagonal matrix A. The factorization may also be regarded as
  having the form A = U'*D*U.

ARGUMENTS
  N	  (input) INTEGER
	  The order of the matrix A.  N >= 0.

  D	  (input/output) DOUBLE PRECISION array, dimension (N)
	  On entry, the n diagonal elements of the tridiagonal matrix A.  On
	  exit, the n diagonal elements of the diagonal matrix D from the
	  L*D*L' factorization of A.

  E	  (input/output) DOUBLE PRECISION array, dimension (N-1)
	  On entry, the (n-1) subdiagonal elements of the tridiagonal matrix
	  A.  On exit, the (n-1) subdiagonal elements of the unit bidiagonal
	  factor L from the L*D*L' factorization of A.	E can also be
	  regarded as the superdiagonal of the unit bidiagonal factor U from
	  the U'*D*U factorization of A.

  INFO	  (output) INTEGER
	  = 0: successful exit
	  < 0: if INFO = -k, the k-th argument had an illegal value
	  > 0: if INFO = k, the leading minor of order k is not positive
	  definite; if k < N, the factorization could not be completed, while
	  if k = N, the factorization was completed, but D(N) = 0.