---
name: "dpttrf"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/dpttrf/3lapack"
---

# dpttrf(3lapack)

computes the L\*D\*L' factorization of a real symmetric positive definite tridiagonal matrix A

## NAME

DPTTRF - computes the L\*D\*L' 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' factorization of a real symmetric positive definite tridiagonal matrix A.  The factorization may also be regarded as having the form A = U'\*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' 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' factorization of A. E can also be regarded as the superdiagonal of the unit bidiagonal factor U from the U'\*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.