DPTTRF - compute the L*D*L' factorization of a real sym
metric 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 symmet
ric positive definite tridiagonal matrix A. The factoriza
tion 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 tridiago
nal matrix A. On exit, the n diagonal elements of
the diagonal matrix D from the L*D*L' factoriza
tion 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) subdiag
onal 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 bidiago
nal 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 ille
gal 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 fac
torization was completed, but D(N) = 0.
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