NAME

DPTTRF - 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.

  —  LAPACK version 2.0  —  08 October 1994