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.


Man(1) output converted with man2html