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 zgttrf.f(3) LAPACK zgttrf.f(3)

zgttrf.f -

# SYNOPSIS

## Functions/Subroutines

subroutine zgttrf (N, DL, D, DU, DU2, IPIV, INFO)

ZGTTRF

# Function/Subroutine Documentation

## subroutine zgttrf (integerN, complex*16, dimension( * )DL, complex*16, dimension( * )D, complex*16, dimension( * )DU, complex*16, dimension( * )DU2, integer, dimension( * )IPIV, integerINFO)

ZGTTRF
Purpose:
``` ZGTTRF computes an LU factorization of a complex 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 COMPLEX*16 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 COMPLEX*16 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 COMPLEX*16 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 COMPLEX*16 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 zgttrf.f.

# Author

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