spttrf(3)

NAME

SPTTRF - compute the L*D*L' factorization of a real sym

metric positive definite tridiagonal matrix A

SYNOPSIS

SUBROUTINE SPTTRF( N, D, E, INFO )
    INTEGER        INFO, N
    REAL           D( * ), E( * )

PURPOSE

SPTTRF computes the L*D*L' factorization of a real symmet

ric 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) REAL 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' factorization of A.

E (input/output) REAL 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 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 factorization was completed, but

D(N) = 0.

LAPACK version 3.0 15 June 2000

SPTTRF(3)