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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 N
*> double precision vector with N elements
*> \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 N
*> double precision vector with N elements
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*> INCY is INTEGER
*> storage spacing between elements of DY
*> \endverbatim
*>
*> \param[in,out] 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.
*
*> \date December 2016
*
*> \ingroup double_blas_level1
*
* =====================================================================
SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
*
* -- Reference BLAS level1 routine (version 3.7.0) --
* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
* December 2016
*
* .. 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
|
