DGTTRF(1) LAPACK routine (version 3.2) DGTTRF(1)NAME
DGTTRF - computes an LU factorization of a real tridiagonal matrix A
using elimination with partial pivoting and row interchanges
SYNOPSIS
SUBROUTINE DGTTRF( N, DL, D, DU, DU2, IPIV, INFO )
INTEGER INFO, N
INTEGER IPIV( * )
DOUBLE PRECISION D( * ), DL( * ), DU( * ), DU2( * )
PURPOSE
DGTTRF computes an LU factorization of a real tridiagonal matrix A
using elimination with partial pivoting and row interchanges. The fac‐
torization has the form
A = L * U
where L is a product of permutation and unit lower bidiagonal matrices
and U is upper triangular with nonzeros in only the main diagonal and
first two superdiagonals.
ARGUMENTS
N (input) INTEGER
The order of the matrix A.
DL (input/output) DOUBLE PRECISION array, dimension (N-1)
On entry, DL must contain the (n-1) sub-diagonal elements of A.
On exit, DL is overwritten by the (n-1) multipliers that define
the matrix L from the LU factorization of A.
D (input/output) DOUBLE PRECISION array, dimension (N)
On entry, D must contain the diagonal elements of A. On exit,
D is overwritten by the n diagonal elements of the upper trian‐
gular matrix U from the LU factorization of A.
DU (input/output) DOUBLE PRECISION array, dimension (N-1)
On entry, DU must contain the (n-1) super-diagonal elements of
A. On exit, DU is overwritten by the (n-1) elements of the
first super-diagonal of U.
DU2 (output) DOUBLE PRECISION array, dimension (N-2)
On exit, DU2 is overwritten by the (n-2) elements of the second
super-diagonal of U.
IPIV (output) INTEGER array, dimension (N)
The pivot indices; for 1 <= i <= n, row i of the matrix was
interchanged with row IPIV(i). IPIV(i) will always be either i
or i+1; IPIV(i) = i indicates a row interchange was not
required.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -k, the k-th argument had an illegal value
> 0: if INFO = k, U(k,k) is exactly zero. The factorization
has been completed, but the factor U is exactly singular, and
division by zero will occur if it is used to solve a system of
equations.
LAPACK routine (version 3.2) November 2008 DGTTRF(1)
