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SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
* .. Scalar Arguments ..
INTEGER INCX,INCY,N
* ..
* .. Array Arguments ..
DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
* ..
*
* Purpose
* =======
*
* 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.
*
* Arguments
* =========
*
* N (input) INTEGER
* number of elements in input vector(s)
*
* DX (input/output) DOUBLE PRECISION array, dimension N
* double precision vector with N elements
*
* INCX (input) INTEGER
* storage spacing between elements of DX
*
* DY (input/output) DOUBLE PRECISION array, dimension N
* double precision vector with N elements
*
* INCY (input) INTEGER
* storage spacing between elements of DY
*
* DPARAM (input/output) DOUBLE PRECISION array, dimension 5
* DPARAM(1)=DFLAG
* DPARAM(2)=DH11
* DPARAM(3)=DH21
* DPARAM(4)=DH12
* DPARAM(5)=DH22
*
* =====================================================================
*
* .. 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
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