# sgttrf(3) [centos man page]

```sgttrf.f(3)							      LAPACK							       sgttrf.f(3)

NAME
sgttrf.f -

SYNOPSIS
Functions/Subroutines
subroutine sgttrf (N, DL, D, DU, DU2, IPIV, INFO)
SGTTRF

Function/Subroutine Documentation
subroutine sgttrf (integerN, real, dimension( * )DL, real, dimension( * )D, real, dimension( * )DU, real, dimension( * )DU2, integer,
dimension( * )IPIV, integerINFO)
SGTTRF

Purpose:

SGTTRF 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 REAL 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 REAL 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 REAL 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 REAL 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

NAG Ltd.

Date:
September 2012

Definition at line 125 of file sgttrf.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       sgttrf.f(3)```

## Check Out this Related Man Page

```SGTTRF(l)								 )								 SGTTRF(l)

NAME
SGTTRF - compute an LU factorization of a real tridiagonal matrix A using elimination with partial pivoting and row interchanges

SYNOPSIS
SUBROUTINE SGTTRF( N, DL, D, DU, DU2, IPIV, INFO )

INTEGER	  INFO, N

INTEGER	  IPIV( * )

REAL 	  D( * ), DL( * ), DU( * ), DU2( * )

PURPOSE
SGTTRF  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) REAL 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) REAL 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      (input/output) REAL 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) REAL 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 version 3.0						   15 June 2000 							 SGTTRF(l)```
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