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

/* Table of constant values */

static integer c__1 = 1;
static double c_b5 = 1.;

/* Subroutine */ int dlarz_(const char *side, integer *m, integer *n, integer *l, 
	double *v, integer *incv, double *tau, double *c__, 
	integer *ldc, double *work)
{
    /* System generated locals */
    integer c_dim1, c_offset;
    double d__1;

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

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

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

/*  DLARZ applies a real elementary reflector H to a real M-by-N */
/*  matrix C, from either the left or the right. H is represented in the */
/*  form */

/*        H = I - tau * v * v' */

/*  where tau is a real scalar and v is a real vector. */

/*  If tau = 0, then H is taken to be the unit matrix. */


/*  H is a product of k elementary reflectors as returned by DTZRZF. */

/*  Arguments */
/*  ========= */

/*  SIDE    (input) CHARACTER*1 */
/*          = 'L': form  H * C */
/*          = 'R': form  C * H */

/*  M       (input) INTEGER */
/*          The number of rows of the matrix C. */

/*  N       (input) INTEGER */
/*          The number of columns of the matrix C. */

/*  L       (input) INTEGER */
/*          The number of entries of the vector V containing */
/*          the meaningful part of the Householder vectors. */
/*          If SIDE = 'L', M >= L >= 0, if SIDE = 'R', N >= L >= 0. */

/*  V       (input) DOUBLE PRECISION array, dimension (1+(L-1)*abs(INCV)) */
/*          The vector v in the representation of H as returned by */
/*          DTZRZF. V is not used if TAU = 0. */

/*  INCV    (input) INTEGER */
/*          The increment between elements of v. INCV <> 0. */

/*  TAU     (input) DOUBLE PRECISION */
/*          The value tau in the representation of H. */

/*  C       (input/output) DOUBLE PRECISION array, dimension (LDC,N) */
/*          On entry, the M-by-N matrix C. */
/*          On exit, C is overwritten by the matrix H * C if SIDE = 'L', */
/*          or C * H if SIDE = 'R'. */

/*  LDC     (input) INTEGER */
/*          The leading dimension of the array C. LDC >= max(1,M). */

/*  WORK    (workspace) DOUBLE PRECISION array, dimension */
/*                         (N) if SIDE = 'L' */
/*                      or (M) if SIDE = 'R' */

/*  Further Details */
/*  =============== */

/*  Based on contributions by */
/*    A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA */

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

/*     .. Parameters .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. Executable Statements .. */

    /* Parameter adjustments */
    --v;
    c_dim1 = *ldc;
    c_offset = 1 + c_dim1;
    c__ -= c_offset;
    --work;

    /* Function Body */
    if (lsame_(side, "L")) {

/*        Form  H * C */

	if (*tau != 0.) {

/*           w( 1:n ) = C( 1, 1:n ) */

	    dcopy_(n, &c__[c_offset], ldc, &work[1], &c__1);

/*           w( 1:n ) = w( 1:n ) + C( m-l+1:m, 1:n )' * v( 1:l ) */

	    dgemv_("Transpose", l, n, &c_b5, &c__[*m - *l + 1 + c_dim1], ldc, 
		    &v[1], incv, &c_b5, &work[1], &c__1);

/*           C( 1, 1:n ) = C( 1, 1:n ) - tau * w( 1:n ) */

	    d__1 = -(*tau);
	    daxpy_(n, &d__1, &work[1], &c__1, &c__[c_offset], ldc);

/*           C( m-l+1:m, 1:n ) = C( m-l+1:m, 1:n ) - ... */
/*                               tau * v( 1:l ) * w( 1:n )' */

	    d__1 = -(*tau);
	    dger_(l, n, &d__1, &v[1], incv, &work[1], &c__1, &c__[*m - *l + 1 
		    + c_dim1], ldc);
	}

    } else {

/*        Form  C * H */

	if (*tau != 0.) {

/*           w( 1:m ) = C( 1:m, 1 ) */

	    dcopy_(m, &c__[c_offset], &c__1, &work[1], &c__1);

/*           w( 1:m ) = w( 1:m ) + C( 1:m, n-l+1:n, 1:n ) * v( 1:l ) */

	    dgemv_("No transpose", m, l, &c_b5, &c__[(*n - *l + 1) * c_dim1 + 
		    1], ldc, &v[1], incv, &c_b5, &work[1], &c__1);

/*           C( 1:m, 1 ) = C( 1:m, 1 ) - tau * w( 1:m ) */

	    d__1 = -(*tau);
	    daxpy_(m, &d__1, &work[1], &c__1, &c__[c_offset], &c__1);

/*           C( 1:m, n-l+1:n ) = C( 1:m, n-l+1:n ) - ... */
/*                               tau * w( 1:m ) * v( 1:l )' */

	    d__1 = -(*tau);
	    dger_(m, l, &d__1, &work[1], &c__1, &v[1], incv, &c__[(*n - *l + 
		    1) * c_dim1 + 1], ldc);

	}

    }

    return 0;

/*     End of DLARZ */

} /* dlarz_ */
