# Ubuntu Feisty 7.04 manual page repository

Ubuntu is a free computer operating system based on the Linux kernel. Many IT companies, like DeployIS is using it to provide an up-to-date, stable operating system.

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` `

### NAME

```        ZDTTRF  - compute an LU factorization of a complex tridiagonal matrix A
using elimination without partial pivoting
```

### SYNOPSIS

```        SUBROUTINE ZDTTRF( N, DL, D, DU, INFO )

INTEGER        INFO, N

COMPLEX*16     D( * ), DL( * ), DU( * )
```

### PURPOSE

```        ZDTTRF computes an LU factorization of a complex tridiagonal  matrix  A
using elimination without partial pivoting.

The factorization has the form
A = L * U
where L is a product of unit lower bidiagonal
matrices and U is upper triangular with nonzeros in only the main diag‐
onal and first superdiagonal.
```

### ARGUMENTS

```        N       (input) INTEGER
The order of the matrix A.  N >= 0.

DL      (input/output) COMPLEX array, dimension (N-1)
On entry, DL must contain the (n-1) subdiagonal 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) COMPLEX 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) COMPLEX array, dimension (N-1)
On entry, DU must contain the (n-1) superdiagonal  elements  of
A.   On  exit,  DU  is overwritten by the (n-1) elements of the
first superdiagonal of U.

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value
> 0:  if INFO = i, U(i,i) 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.

```
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