dgeqr2 man page on YellowDog

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DGEQR2(l)			       )			     DGEQR2(l)

NAME
       DGEQR2 - compute a QR factorization of a real m by n matrix A

SYNOPSIS
       SUBROUTINE DGEQR2( M, N, A, LDA, TAU, WORK, INFO )

	   INTEGER	  INFO, LDA, M, N

	   DOUBLE	  PRECISION A( LDA, * ), TAU( * ), WORK( * )

PURPOSE
       DGEQR2  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) DOUBLE PRECISION 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 triangular 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 dimenā€
	       sion of the array A.  LDA >= max(1,M).

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

       WORK    (workspace) DOUBLE PRECISION 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			     DGEQR2(l)
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