DPTTRF (3lapack)

compute the 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 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) 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**T factorization of A.

  E       (input/output) DOUBLE PRECISION 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.