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NAME
     dpttrf - compute the factorization of a real symmetric posi-
     tive definite tridiagonal matrix A

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

     INTEGER INFO, N

     DOUBLE PRECISION D( * ), E( * )



     #include <sunperf.h>

     void dpttrf(int n, double *d, double *e, int *info) ;

PURPOSE
     DPTTRF computes the factorization of a real symmetric  posi-
     tive 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  superdiago-
     nal  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 tridiago-
               nal matrix A.  On exit, the n diagonal elements of
               the diagonal matrix D from the L*D*L**T factoriza-
               tion 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 ille-
               gal 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  fac-
               torization was completed, but D(N) = 0.

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