!>
!> DPTTRF computes the L*D*L**T factorization of a real symmetric
!> positive definite tridiagonal matrix A.  The factorization may also
!> be regarded as having the form A = U**T*D*U.
!> 

N

!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!> 

D

!>          D is 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

!>          E is DOUBLE PRECISION 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**T factorization of A.
!>          E can also be regarded as the superdiagonal of the unit
!>          bidiagonal factor U from the U**T*D*U factorization of A.
!> 

INFO

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

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