#include "clapack.h"
#include "f2cP.h"

/* Table of constant values */

static integer c__1 = 1;
static integer c_n1 = -1;
static integer c__3 = 3;
static integer c__2 = 2;

/* Subroutine */ int dgerqf_(integer *m, integer *n, double *a, integer *
	lda, double *tau, double *work, integer *lwork, integer *info)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3, i__4;

    /* Local variables */
    integer i__, k, ib, nb, ki, kk, mu, nu, nx, iws, nbmin, iinfo;
    integer ldwork, lwkopt;
    bool lquery;


/*  -- LAPACK routine (version 3.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  DGERQF computes an RQ factorization of a real M-by-N matrix A: */
/*  A = R * 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, */
/*          if m <= n, the upper triangle of the subarray */
/*          A(1:m,n-m+1:n) contains the M-by-M upper triangular matrix R; */
/*          if m >= n, the elements on and above the (m-n)-th subdiagonal */
/*          contain the M-by-N upper trapezoidal matrix R; */
/*          the remaining elements, 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 (MAX(1,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(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(n-k+i+1:n) = 0 and v(n-k+i) = 1; v(1:n-k+i-1) is stored on exit in */
/*  A(m-k+i,1:n-k+i-1), and tau in TAU(i). */

/*  ===================================================================== */

/*     .. Local Scalars .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. Executable Statements .. */

/*     Test the input arguments */

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

    /* Function Body */
    *info = 0;
    lquery = *lwork == -1;
    if (*m < 0) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*lda < std::max(1_integer,*m)) {
	*info = -4;
    }

    if (*info == 0) {
	k = std::min(*m,*n);
	if (k == 0) {
	    lwkopt = 1;
	} else {
	    nb = ilaenv_(&c__1, "DGERQF", " ", m, n, &c_n1, &c_n1);
	    lwkopt = *m * nb;
	}
	work[1] = (double) lwkopt;

	if (*lwork < std::max(1_integer,*m) && ! lquery) {
	    *info = -7;
	}
    }

    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DGERQF", &i__1);
	return 0;
    } else if (lquery) {
	return 0;
    }

/*     Quick return if possible */

    if (k == 0) {
	return 0;
    }

    nbmin = 2;
    nx = 1;
    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, "DGERQF", " ", m, n, &c_n1, &c_n1);
	nx = std::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, "DGERQF", " ", m, n, &c_n1, &
			c_n1);
		nbmin = std::max(i__1,i__2);
	    }
	}
    }

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

/*        Use blocked code initially. */
/*        The last kk rows are handled by the block method. */

	ki = (k - nx - 1) / nb * nb;
/* Computing MIN */
	i__1 = k, i__2 = ki + nb;
	kk = std::min(i__1,i__2);

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

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

	    i__3 = *n - k + i__ + ib - 1;
	    dgerq2_(&ib, &i__3, &a[*m - k + i__ + a_dim1], lda, &tau[i__], &
		    work[1], &iinfo);
	    if (*m - k + i__ > 1) {

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

		i__3 = *n - k + i__ + ib - 1;
		dlarft_("Backward", "Rowwise", &i__3, &ib, &a[*m - k + i__ + 
			a_dim1], lda, &tau[i__], &work[1], &ldwork);

/*              Apply H to A(1:m-k+i-1,1:n-k+i+ib-1) from the right */

		i__3 = *m - k + i__ - 1;
		i__4 = *n - k + i__ + ib - 1;
		dlarfb_("Right", "No transpose", "Backward", "Rowwise", &i__3, 
			 &i__4, &ib, &a[*m - k + i__ + a_dim1], lda, &work[1], 
			 &ldwork, &a[a_offset], lda, &work[ib + 1], &ldwork);
	    }
/* L10: */
	}
	mu = *m - k + i__ + nb - 1;
	nu = *n - k + i__ + nb - 1;
    } else {
	mu = *m;
	nu = *n;
    }

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

    if (mu > 0 && nu > 0) {
	dgerq2_(&mu, &nu, &a[a_offset], lda, &tau[1], &work[1], &iinfo);
    }

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

/*     End of DGERQF */

} /* dgerqf_ */
