Provided by: liblapack-doc_3.3.1-1_all

**NAME**

LAPACK-3 - computes the L*D*L**T 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 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.

**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) 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 (output) INTEGER = 0: successful exit < 0: if INFO = -k, the k-th argument had an illegal value > 0: if INFO = k, the leading minor of order k is not positive definite; if k < N, the factorization could not be completed, while if k = N, the factorization was completed, but D(N) <= 0. LAPACK routine (version 3.3.1) April 2011 DPTTRF(3lapack)