/* Copyright (c) 1992-2008 The University of Tennessee.  All rights reserved.
 * See file COPYING in this directory for details. */

#ifdef __cplusplus
extern "C" {
#endif

#include "f2c.h"
#include "hypre_lapack.h"

/* Subroutine */ integer dgeqr2_(integer *m, integer *n, doublereal *a, integer *
	lda, doublereal *tau, doublereal *work, integer *info)
{
/*  -- LAPACK routine (version 3.0) --
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
       Courant Institute, Argonne National Lab, and Rice University
       February 29, 1992


    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 dimension 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).

    =====================================================================


       Test the input arguments

       Parameter adjustments */
    /* Table of constant values */
    integer c__1 = 1;

    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3;
    /* Local variables */
    integer i__, k;
    extern /* Subroutine */ integer dlarf_(const char *, integer *, integer *,
	    doublereal *, integer *, doublereal *, doublereal *, integer *,
	    doublereal *), dlarfg_(integer *, doublereal *,
	    doublereal *, integer *, doublereal *), xerbla_(const char *, integer *);
    doublereal aii;
#define a_ref(a_1,a_2) a[(a_2)*a_dim1 + a_1]


    a_dim1 = *lda;
    a_offset = 1 + a_dim1 * 1;
    a -= a_offset;
    --tau;
    --work;

    /* Function Body */
    *info = 0;
    if (*m < 0) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*lda < max(1,*m)) {
	*info = -4;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DGEQR2", &i__1);
	return 0;
    }

    k = min(*m,*n);

    i__1 = k;
    for (i__ = 1; i__ <= i__1; ++i__) {

/*        Generate elementary reflector H(i) to annihilate A(i+1:m,i)

   Computing MIN */
	i__2 = i__ + 1;
	i__3 = *m - i__ + 1;
	dlarfg_(&i__3, &a_ref(i__, i__), &a_ref(min(i__2,*m), i__), &c__1, &
		tau[i__]);
	if (i__ < *n) {

/*           Apply H(i) to A(i:m,i+1:n) from the left */

	    aii = a_ref(i__, i__);
	    a_ref(i__, i__) = 1.;
	    i__2 = *m - i__ + 1;
	    i__3 = *n - i__;
	    dlarf_("Left", &i__2, &i__3, &a_ref(i__, i__), &c__1, &tau[i__], &
		    a_ref(i__, i__ + 1), lda, &work[1]);
	    a_ref(i__, i__) = aii;
	}
/* L10: */
    }
    return 0;

/*     End of DGEQR2 */

} /* dgeqr2_ */

#undef a_ref

#ifdef __cplusplus
}
#endif
