# RedHat 9 (Linux i386) - man page for cgeqr2 (redhat section l)

```CGEQR2(l)								 )								 CGEQR2(l)

NAME
CGEQR2 - compute a QR factorization of a complex m by n matrix A

SYNOPSIS
SUBROUTINE CGEQR2( M, N, A, LDA, TAU, WORK, INFO )

INTEGER	  INFO, LDA, M, N

COMPLEX	  A( LDA, * ), TAU( * ), WORK( * )

PURPOSE
CGEQR2 computes a QR factorization of a complex m by n matrix A: A = Q * R.

ARGUMENTS
M       (input) INTEGER
The number of rows of the matrix A.  M &gt;= 0.

N       (input) INTEGER
The number of columns of the matrix A.  N &gt;= 0.

A       (input/output) COMPLEX array, dimension (LDA,N)
On entry, the m by n matrix A.  On exit, the elements on and above the diagonal of the array contain the min(m,n) by n upper trape-
zoidal matrix R (R is upper triangular if m &gt;= n); the elements below the diagonal, with  the  array  TAU,  represent  the  unitary
matrix  Q  as a product of elementary reflectors (see Further Details).	LDA	(input) INTEGER The leading dimension of the array
A.  LDA &gt;= max(1,M).

TAU     (output) COMPLEX array, dimension (min(M,N))
The scalar factors of the elementary reflectors (see Further Details).

WORK    (workspace) COMPLEX array, dimension (N)

INFO    (output) INTEGER
= 0: successful exit
&lt; 0: if INFO = -i, the i-th argument had an illegal value

FURTHER DETAILS
The matrix Q is represented as a product of elementary reflectors

Q = H(1) H(2) . . . H(k), where k = min(m,n).

Each H(i) has the form

H(i) = I - tau * v * v&#039;

where tau is a complex scalar, and v is a complex vector with v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i), and  tau
in TAU(i).

LAPACK version 3.0						   15 June 2000 							 CGEQR2(l)```