201 lines
5.1 KiB
Fortran
201 lines
5.1 KiB
Fortran
*> \brief \b DROTM
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
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*
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* .. Scalar Arguments ..
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* INTEGER INCX,INCY,N
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
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*>
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*> (DX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF DX ARE IN
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*> (DY**T)
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*>
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*> DX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
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*> LX = (-INCX)*N, AND SIMILARLY FOR SY USING LY AND INCY.
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*> WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
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*>
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*> DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0
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*>
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*> (DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0)
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*> H=( ) ( ) ( ) ( )
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*> (DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0).
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*> SEE DROTMG FOR A DESCRIPTION OF DATA STORAGE IN DPARAM.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> number of elements in input vector(s)
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*> \endverbatim
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*>
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*> \param[in,out] DX
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*> \verbatim
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*> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> storage spacing between elements of DX
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*> \endverbatim
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*>
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*> \param[in,out] DY
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*> \verbatim
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*> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
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*> \endverbatim
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*>
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*> \param[in] INCY
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*> \verbatim
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*> INCY is INTEGER
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*> storage spacing between elements of DY
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*> \endverbatim
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*>
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*> \param[in] DPARAM
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*> \verbatim
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*> DPARAM is DOUBLE PRECISION array, dimension (5)
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*> DPARAM(1)=DFLAG
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*> DPARAM(2)=DH11
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*> DPARAM(3)=DH21
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*> DPARAM(4)=DH12
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*> DPARAM(5)=DH22
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date November 2017
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*
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*> \ingroup double_blas_level1
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*
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* =====================================================================
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SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
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*
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* -- Reference BLAS level1 routine (version 3.8.0) --
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* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* November 2017
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*
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* .. Scalar Arguments ..
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INTEGER INCX,INCY,N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
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* ..
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,TWO,W,Z,ZERO
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INTEGER I,KX,KY,NSTEPS
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* ..
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* .. Data statements ..
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DATA ZERO,TWO/0.D0,2.D0/
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* ..
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*
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DFLAG = DPARAM(1)
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IF (N.LE.0 .OR. (DFLAG+TWO.EQ.ZERO)) RETURN
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IF (INCX.EQ.INCY.AND.INCX.GT.0) THEN
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*
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NSTEPS = N*INCX
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IF (DFLAG.LT.ZERO) THEN
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DH11 = DPARAM(2)
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DH12 = DPARAM(4)
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DH21 = DPARAM(3)
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DH22 = DPARAM(5)
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DO I = 1,NSTEPS,INCX
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W = DX(I)
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Z = DY(I)
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DX(I) = W*DH11 + Z*DH12
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DY(I) = W*DH21 + Z*DH22
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END DO
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ELSE IF (DFLAG.EQ.ZERO) THEN
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DH12 = DPARAM(4)
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DH21 = DPARAM(3)
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DO I = 1,NSTEPS,INCX
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W = DX(I)
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Z = DY(I)
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DX(I) = W + Z*DH12
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DY(I) = W*DH21 + Z
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END DO
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ELSE
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DH11 = DPARAM(2)
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DH22 = DPARAM(5)
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DO I = 1,NSTEPS,INCX
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W = DX(I)
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Z = DY(I)
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DX(I) = W*DH11 + Z
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DY(I) = -W + DH22*Z
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END DO
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END IF
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ELSE
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KX = 1
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KY = 1
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IF (INCX.LT.0) KX = 1 + (1-N)*INCX
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IF (INCY.LT.0) KY = 1 + (1-N)*INCY
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*
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IF (DFLAG.LT.ZERO) THEN
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DH11 = DPARAM(2)
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DH12 = DPARAM(4)
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DH21 = DPARAM(3)
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DH22 = DPARAM(5)
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DO I = 1,N
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W = DX(KX)
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Z = DY(KY)
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DX(KX) = W*DH11 + Z*DH12
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DY(KY) = W*DH21 + Z*DH22
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KX = KX + INCX
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KY = KY + INCY
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END DO
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ELSE IF (DFLAG.EQ.ZERO) THEN
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DH12 = DPARAM(4)
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DH21 = DPARAM(3)
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DO I = 1,N
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W = DX(KX)
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Z = DY(KY)
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DX(KX) = W + Z*DH12
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DY(KY) = W*DH21 + Z
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KX = KX + INCX
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KY = KY + INCY
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END DO
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ELSE
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DH11 = DPARAM(2)
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DH22 = DPARAM(5)
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DO I = 1,N
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W = DX(KX)
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Z = DY(KY)
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DX(KX) = W*DH11 + Z
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DY(KY) = -W + DH22*Z
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KX = KX + INCX
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KY = KY + INCY
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END DO
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END IF
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END IF
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RETURN
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END
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