# sgttrf.f man page

sgttrf.f —

## Synopsis

### Functions/Subroutines

subroutinesgttrf(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

Univ. of Colorado Denver

NAG Ltd.

**Date:**

September 2012

Definition at line 125 of file sgttrf.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

sgttrf(3) is an alias of sgttrf.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK