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RedHat 9 (Linux i386) - man page for sgeqr2 (redhat section l)

SGEQR2(l)					)					SGEQR2(l)

NAME
       SGEQR2 - compute a QR factorization of a real m by n matrix A

SYNOPSIS
       SUBROUTINE SGEQR2( M, N, A, LDA, TAU, WORK, INFO )

	   INTEGER	  INFO, LDA, M, N

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

PURPOSE
       SGEQR2 computes a QR factorization of a real m by n matrix A: A = Q * R.

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) REAL 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 trapezoidal matrix R (R is upper  trian-
	       gular  if  m >= n); the elements below the diagonal, with the array TAU, represent
	       the orthogonal matrix Q	as  a  product	of  elementary	reflectors  (see  Further
	       Details).   LDA	    (input) INTEGER The leading dimension of the array A.  LDA >=
	       max(1,M).

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

       WORK    (workspace) REAL array, dimension (N)

       INFO    (output) INTEGER
	       = 0: successful exit
	       < 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'

       where tau is a real scalar, and v is a real 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 				SGEQR2(l)


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