/* 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 dgeqrf_(integer *m, integer *n, doublereal *a, integer *
	lda, doublereal *tau, doublereal *work, integer *lwork, integer *info)
{
/*  -- LAPACK routine (version 3.0) --
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
       Courant Institute, Argonne National Lab, and Rice University
       June 30, 1999


    Purpose
    =======

    DGEQRF 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 min(m,n) 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/output) DOUBLE PRECISION array, dimension (LWORK)
            On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

    LWORK   (input) INTEGER
            The dimension of the array WORK.  LWORK >= max(1,N).
            For optimum performance LWORK >= N*NB, where NB is
            the optimal blocksize.

            If LWORK = -1, then a workspace query is assumed; the routine
            only calculates the optimal size of the WORK array, returns
            this value as the first entry of the WORK array, and no error
            message related to LWORK is issued by XERBLA.

    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;
    integer c_n1 = -1;
    integer c__3 = 3;
    integer c__2 = 2;

    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3, i__4;
    /* Local variables */
    integer i__, k, nbmin, iinfo;
    extern /* Subroutine */ integer dgeqr2_(integer *, integer *, doublereal *,
	    integer *, doublereal *, doublereal *, integer *);
    integer ib, nb;
    extern /* Subroutine */ integer dlarfb_(const char *,const char *,const char *,const char *,
	    integer *, integer *, integer *, doublereal *, integer *,
	    doublereal *, integer *, doublereal *, integer *, doublereal *,
	    integer *);
    integer nx;
    extern /* Subroutine */ integer dlarft_(const char *,const char *, integer *, integer *,
	    doublereal *, integer *, doublereal *, doublereal *, integer *), xerbla_(const char *, integer *);
    extern integer ilaenv_(integer *,const char *,const char *, integer *, integer *,
	    integer *, integer *, ftnlen, ftnlen);
    integer ldwork, lwkopt;
    logical lquery;
    integer iws;
#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;
    nb = ilaenv_(&c__1, "DGEQRF", " ", m, n, &c_n1, &c_n1, (ftnlen)6, (ftnlen)
	    1);
    lwkopt = *n * nb;
    work[1] = (doublereal) lwkopt;
    lquery = *lwork == -1;
    if (*m < 0) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*lda < max(1,*m)) {
	*info = -4;
    } else if (*lwork < max(1,*n) && ! lquery) {
	*info = -7;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DGEQRF", &i__1);
	return 0;
    } else if (lquery) {
	return 0;
    }

/*     Quick return if possible */

    k = min(*m,*n);
    if (k == 0) {
	work[1] = 1.;
	return 0;
    }

    nbmin = 2;
    nx = 0;
    iws = *n;
    if (nb > 1 && nb < k) {

/*        Determine when to cross over from blocked to unblocked code.

   Computing MAX */
	i__1 = 0, i__2 = ilaenv_(&c__3, "DGEQRF", " ", m, n, &c_n1, &c_n1, (
		ftnlen)6, (ftnlen)1);
	nx = max(i__1,i__2);
	if (nx < k) {

/*           Determine if workspace is large enough for blocked code. */

	    ldwork = *n;
	    iws = ldwork * nb;
	    if (*lwork < iws) {

/*              Not enough workspace to use optimal NB:  reduce NB and
                determine the minimum value of NB. */

		nb = *lwork / ldwork;
/* Computing MAX */
		i__1 = 2, i__2 = ilaenv_(&c__2, "DGEQRF", " ", m, n, &c_n1, &
			c_n1, (ftnlen)6, (ftnlen)1);
		nbmin = max(i__1,i__2);
	    }
	}
    }

    if (nb >= nbmin && nb < k && nx < k) {

/*        Use blocked code initially */

	i__1 = k - nx;
	i__2 = nb;
	for (i__ = 1; i__2 < 0 ? i__ >= i__1 : i__ <= i__1; i__ += i__2) {
/* Computing MIN */
	    i__3 = k - i__ + 1;
	    ib = min(i__3,nb);

/*           Compute the QR factorization of the current block
             A(i:m,i:i+ib-1) */

	    i__3 = *m - i__ + 1;
	    dgeqr2_(&i__3, &ib, &a_ref(i__, i__), lda, &tau[i__], &work[1], &
		    iinfo);
	    if (i__ + ib <= *n) {

/*              Form the triangular factor of the block reflector
                H = H(i) H(i+1) . . . H(i+ib-1) */

		i__3 = *m - i__ + 1;
		dlarft_("Forward", "Columnwise", &i__3, &ib, &a_ref(i__, i__),
			 lda, &tau[i__], &work[1], &ldwork);

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

		i__3 = *m - i__ + 1;
		i__4 = *n - i__ - ib + 1;
		dlarfb_("Left", "Transpose", "Forward", "Columnwise", &i__3, &
			i__4, &ib, &a_ref(i__, i__), lda, &work[1], &ldwork, &
			a_ref(i__, i__ + ib), lda, &work[ib + 1], &ldwork);
	    }
/* L10: */
	}
    } else {
	i__ = 1;
    }

/*     Use unblocked code to factor the last or only block. */

    if (i__ <= k) {
	i__2 = *m - i__ + 1;
	i__1 = *n - i__ + 1;
	dgeqr2_(&i__2, &i__1, &a_ref(i__, i__), lda, &tau[i__], &work[1], &
		iinfo);
    }

    work[1] = (doublereal) iws;
    return 0;

/*     End of DGEQRF */

} /* dgeqrf_ */

#undef a_ref

#ifdef __cplusplus
}
#endif
