spttrf(3F)

NAME
     SPTTRF - compute the factorization of a real symmetric positive definite
     tridiagonal matrix A

SYNOPSIS
     SUBROUTINE SPTTRF( N, D, E, INFO )

         INTEGER        INFO, N

         REAL           D( * ), E( * )

PURPOSE
     SPTTRF computes the factorization of a real symmetric positive definite
     tridiagonal matrix A.

     If the subdiagonal elements of A are supplied in the array E, the
     factorization has the form A = L*D*L**T, where D is diagonal and L is
     unit lower bidiagonal; if the superdiagonal elements of A are supplied,
     it has the form A = U**T*D*U, where U is unit upper bidiagonal.  (The two
     forms are equivalent if A is real.)


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 tridiagonal matrix A.
             On exit, the n diagonal elements of the diagonal matrix D from
             the L*D*L**T factorization of A.

     E       (input/output) REAL array, dimension (N-1)
             On entry, the (n-1) off-diagonal elements of the tridiagonal
             matrix A.  On exit, the (n-1) off-diagonal elements of the unit
             bidiagonal factor L or U from the factorization of A.

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