dgetf2(3)

NAME

DGETF2 - compute an LU factorization of a general m-by-n

matrix A using partial pivoting with row interchanges

SYNOPSIS

SUBROUTINE DGETF2( M, N, A, LDA, IPIV, INFO )
    INTEGER        INFO, LDA, M, N
    INTEGER        IPIV( * )
    DOUBLE         PRECISION A( LDA, * )

PURPOSE

DGETF2 computes an LU factorization of a general m-by-n

matrix A using partial pivoting with row interchanges. The fac

torization has the form

A = P * L * U

where P is a permutation matrix, L is lower triangular

with unit diagonal elements (lower trapezoidal if m > n), and U

is upper triangular (upper trapezoidal if m < n).

This is the right-looking Level 2 BLAS version of the al

gorithm.

ARGUMENTS

M (input) INTEGER

The number of rows of the matrix A. M >= 0.

N (input) INTEGER

The number of columns of the matrix A. N >= 0.

A (input/output) DOUBLE PRECISION array, dimension

(LDA,N)

On entry, the m by n matrix to be factored. On

exit, the factors L and U from the factorization A = P*L*U; the

unit diagonal elements of L are not stored.

LDA (input) INTEGER

The leading dimension of the array A. LDA >=

max(1,M).

IPIV (output) INTEGER array, dimension (min(M,N))

The pivot indices; for 1 <= i <= min(M,N), row i

of the matrix was interchanged with row IPIV(i).

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -k, the k-th argument had an ille

gal value
> 0: if INFO = k, U(k,k) is exactly zero. The fac

torization has been completed, but the factor U is exactly singu

lar, and division by zero will occur if it is used to solve a

system of equations.

LAPACK version 3.0 15 June 2000

DGETF2(3)