dgttrf.f(3) LAPACK dgttrf.f(3)
NAME
dgttrf.f -
SYNOPSIS
Functions/Subroutines
subroutine dgttrf (N, DL, D, DU, DU2, IPIV, INFO)
DGTTRF
Function/Subroutine Documentation
subroutine dgttrf (integerN, double precision, dimension( * )DL, double precision, dimension( * )D, double precision, dimension( * )DU, double
precision, dimension( * )DU2, integer, dimension( * )IPIV, integerINFO)
DGTTRF
Purpose:
DGTTRF computes an LU factorization of a real tridiagonal matrix A
using elimination with partial pivoting and row interchanges.
The factorization 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.
Parameters:
N
N is INTEGER
The order of the matrix A.
DL
DL is 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
D is 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 triangular matrix U from the LU factorization of A.
DU
DU is 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
DU2 is DOUBLE PRECISION array, dimension (N-2)
On exit, DU2 is overwritten by the (n-2) elements of the
second super-diagonal of U.
IPIV
IPIV is 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
INFO is 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.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Definition at line 125 of file dgttrf.f.
Author
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Version 3.4.1 Sun May 26 2013 dgttrf.f(3)