# sgttrf.f man page

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

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