DPTTRF(3)
computes the L*D*L' factorization of a real symmetric positive definite tridiagonal matrix A
SYNOPSIS
 SUBROUTINE DPTTRF(

N, D, E, INFO )

INTEGER
INFO, N

DOUBLE
PRECISION D( * ), E( * )
PURPOSE
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 (N1)

On entry, the (n1) subdiagonal elements of the tridiagonal
matrix A. On exit, the (n1) 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 kth 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.