dgttrf(3P) Sun Performance Library dgttrf(3P)NAMEdgttrf - compute an LU factorization of a real tridiagonal matrix A
using elimination with partial pivoting and row interchanges
SYNOPSIS
SUBROUTINE DGTTRF(N, LOW, D, UP1, UP2, IPIVOT, INFO)
INTEGER N, INFO
INTEGER IPIVOT(*)
DOUBLE PRECISION LOW(*), D(*), UP1(*), UP2(*)
SUBROUTINE DGTTRF_64(N, LOW, D, UP1, UP2, IPIVOT, INFO)
INTEGER*8 N, INFO
INTEGER*8 IPIVOT(*)
DOUBLE PRECISION LOW(*), D(*), UP1(*), UP2(*)
F95 INTERFACE
SUBROUTINE GTTRF([N], LOW, D, UP1, UP2, IPIVOT, [INFO])
INTEGER :: N, INFO
INTEGER, DIMENSION(:) :: IPIVOT
REAL(8), DIMENSION(:) :: LOW, D, UP1, UP2
SUBROUTINE GTTRF_64([N], LOW, D, UP1, UP2, IPIVOT, [INFO])
INTEGER(8) :: N, INFO
INTEGER(8), DIMENSION(:) :: IPIVOT
REAL(8), DIMENSION(:) :: LOW, D, UP1, UP2
C INTERFACE
#include <sunperf.h>
void dgttrf(int n, double *low, double *d, double *up1, double *up2,
int *ipivot, int *info);
void dgttrf_64(long n, double *low, double *d, double *up1, double
*up2, long *ipivot, long *info);
PURPOSEdgttrf 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.
ARGUMENTS
N (input) The order of the matrix A.
LOW (input/output)
On entry, LOW must contain the (n-1) sub-diagonal elements of
A.
On exit, LOW is overwritten by the (n-1) multipliers that
define the matrix L from the LU factorization of A.
D (input/output)
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.
UP1 (input/output)
On entry, UP1 must contain the (n-1) super-diagonal elements
of A.
On exit, UP1 is overwritten by the (n-1) elements of the
first super-diagonal of U.
UP2 (output)
On exit, UP2 is overwritten by the (n-2) elements of the sec‐
ond super-diagonal of U.
IPIVOT (output)
The pivot indices; for 1 <= i <= n, row i of the matrix was
interchanged with row IPIVOT(i). IPIVOT(i) will always be
either i or i+1; IPIVOT(i) = i indicates a row interchange
was not required.
INFO (output)
= 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.
6 Mar 2009 dgttrf(3P)
