drotm.f

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*> \brief \b DROTM
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
*
*       .. Scalar Arguments ..
*       INTEGER INCX,INCY,N
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*>    APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
*>
*>    (DX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF DX ARE IN
*>    (DY**T)
*>
*>    DX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
*>    LX = (-INCX)*N, AND SIMILARLY FOR SY USING LY AND INCY.
*>    WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
*>
*>    DFLAG=-1.D0     DFLAG=0.D0        DFLAG=1.D0     DFLAG=-2.D0
*>
*>      (DH11  DH12)    (1.D0  DH12)    (DH11  1.D0)    (1.D0  0.D0)
*>    H=(          )    (          )    (          )    (          )
*>      (DH21  DH22),   (DH21  1.D0),   (-1.D0 DH22),   (0.D0  1.D0).
*>    SEE DROTMG FOR A DESCRIPTION OF DATA STORAGE IN DPARAM.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>         number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in,out] DX
*> \verbatim
*>          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>         storage spacing between elements of DX
*> \endverbatim
*>
*> \param[in,out] DY
*> \verbatim
*>          DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*>          INCY is INTEGER
*>         storage spacing between elements of DY
*> \endverbatim
*>
*> \param[in] DPARAM
*> \verbatim
*>          DPARAM is DOUBLE PRECISION array, dimension (5)
*>     DPARAM(1)=DFLAG
*>     DPARAM(2)=DH11
*>     DPARAM(3)=DH21
*>     DPARAM(4)=DH12
*>     DPARAM(5)=DH22
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup rotm
*
*  =====================================================================
      SUBROUTINE drotm(N,DX,INCX,DY,INCY,DPARAM)
*
*  -- Reference BLAS level1 routine --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER INCX,INCY,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,TWO,W,Z,ZERO
      INTEGER I,KX,KY,NSTEPS
*     ..
*     .. Data statements ..
      DATA zero,two/0.d0,2.d0/
*     ..
*
      dflag = dparam(1)
      IF (n.LE.0 .OR. (dflag+two.EQ.zero)) RETURN
      IF (incx.EQ.incy.AND.incx.GT.0) THEN
*
         nsteps = n*incx
         IF (dflag.LT.zero) THEN
            dh11 = dparam(2)
            dh12 = dparam(4)
            dh21 = dparam(3)
            dh22 = dparam(5)
            DO i = 1,nsteps,incx
               w = dx(i)
               z = dy(i)
               dx(i) = w*dh11 + z*dh12
               dy(i) = w*dh21 + z*dh22
            END DO
         ELSE IF (dflag.EQ.zero) THEN
            dh12 = dparam(4)
            dh21 = dparam(3)
            DO i = 1,nsteps,incx
               w = dx(i)
               z = dy(i)
               dx(i) = w + z*dh12
               dy(i) = w*dh21 + z
            END DO
         ELSE
            dh11 = dparam(2)
            dh22 = dparam(5)
            DO i = 1,nsteps,incx
               w = dx(i)
               z = dy(i)
               dx(i) = w*dh11 + z
               dy(i) = -w + dh22*z
            END DO
         END IF
      ELSE
         kx = 1
         ky = 1
         IF (incx.LT.0) kx = 1 + (1-n)*incx
         IF (incy.LT.0) ky = 1 + (1-n)*incy
*
         IF (dflag.LT.zero) THEN
            dh11 = dparam(2)
            dh12 = dparam(4)
            dh21 = dparam(3)
            dh22 = dparam(5)
            DO i = 1,n
               w = dx(kx)
               z = dy(ky)
               dx(kx) = w*dh11 + z*dh12
               dy(ky) = w*dh21 + z*dh22
               kx = kx + incx
               ky = ky + incy
            END DO
         ELSE IF (dflag.EQ.zero) THEN
            dh12 = dparam(4)
            dh21 = dparam(3)
            DO i = 1,n
               w = dx(kx)
               z = dy(ky)
               dx(kx) = w + z*dh12
               dy(ky) = w*dh21 + z
               kx = kx + incx
               ky = ky + incy
            END DO
         ELSE
             dh11 = dparam(2)
             dh22 = dparam(5)
             DO i = 1,n
                w = dx(kx)
                z = dy(ky)
                dx(kx) = w*dh11 + z
                dy(ky) = -w + dh22*z
                kx = kx + incx
                ky = ky + incy
            END DO
         END IF
      END IF
      RETURN
*
*     End of DROTM
*
      END