/* 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 dgelqf_(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   
    =======   

    DGELQF computes an LQ factorization of a real M-by-N matrix A:   
    A = L * Q.   

    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 below the diagonal of the array   
            contain the m-by-min(m,n) lower trapezoidal matrix L (L is   
            lower triangular if m <= n); the elements above 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/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,M).   
            For optimum performance LWORK >= M*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(k) . . . H(2) H(1), 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:n) is stored on exit in A(i,i+1:n),   
    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 dgelq2_(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, "DGELQF", " ", m, n, &c_n1, &c_n1, (ftnlen)6, (ftnlen)
	    1);
    lwkopt = *m * 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,*m) && ! lquery) {
	*info = -7;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DGELQF", &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 = *m;
    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, "DGELQF", " ", 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 = *m;
	    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, "DGELQF", " ", 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 LQ factorization of the current block   
             A(i:i+ib-1,i:n) */

	    i__3 = *n - i__ + 1;
	    dgelq2_(&ib, &i__3, &a_ref(i__, i__), lda, &tau[i__], &work[1], &
		    iinfo);
	    if (i__ + ib <= *m) {

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

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

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

		i__3 = *m - i__ - ib + 1;
		i__4 = *n - i__ + 1;
		dlarfb_("Right", "No transpose", "Forward", "Rowwise", &i__3, 
			&i__4, &ib, &a_ref(i__, i__), lda, &work[1], &ldwork, 
			&a_ref(i__ + ib, i__), 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;
	dgelq2_(&i__2, &i__1, &a_ref(i__, i__), lda, &tau[i__], &work[1], &
		iinfo);
    }

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

/*     End of DGELQF */

} /* dgelqf_ */

#undef a_ref

#ifdef __cplusplus
}
#endif
