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SUBROUTINE SROTM(N,SX,INCX,SY,INCY,SPARAM)
* .. Scalar Arguments ..
INTEGER INCX,INCY,N
* ..
* .. Array Arguments ..
REAL SPARAM(5),SX(*),SY(*)
* ..
*
* Purpose
* =======
*
* APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
*
* (SX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF SX ARE IN
* (SX**T)
*
* SX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
* LX = (-INCX)*N, AND SIMILARLY FOR SY USING USING LY AND INCY.
* WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..
*
* SFLAG=-1.E0 SFLAG=0.E0 SFLAG=1.E0 SFLAG=-2.E0
*
* (SH11 SH12) (1.E0 SH12) (SH11 1.E0) (1.E0 0.E0)
* H=( ) ( ) ( ) ( )
* (SH21 SH22), (SH21 1.E0), (-1.E0 SH22), (0.E0 1.E0).
* SEE SROTMG FOR A DESCRIPTION OF DATA STORAGE IN SPARAM.
*
*
* Arguments
* =========
*
* N (input) INTEGER
* number of elements in input vector(s)
*
* SX (input/output) REAL array, dimension N
* double precision vector with N elements
*
* INCX (input) INTEGER
* storage spacing between elements of SX
*
* SY (input/output) REAL array, dimension N
* double precision vector with N elements
*
* INCY (input) INTEGER
* storage spacing between elements of SY
*
* SPARAM (input/output) REAL array, dimension 5
* SPARAM(1)=SFLAG
* SPARAM(2)=SH11
* SPARAM(3)=SH21
* SPARAM(4)=SH12
* SPARAM(5)=SH22
*
* =====================================================================
*
* .. Local Scalars ..
REAL SFLAG,SH11,SH12,SH21,SH22,TWO,W,Z,ZERO
INTEGER I,KX,KY,NSTEPS
* ..
* .. Data statements ..
DATA ZERO,TWO/0.E0,2.E0/
* ..
*
SFLAG = SPARAM(1)
IF (N.LE.0 .OR. (SFLAG+TWO.EQ.ZERO)) RETURN
IF (INCX.EQ.INCY.AND.INCX.GT.0) THEN
*
NSTEPS = N*INCX
IF (SFLAG.LT.ZERO) THEN
SH11 = SPARAM(2)
SH12 = SPARAM(4)
SH21 = SPARAM(3)
SH22 = SPARAM(5)
DO I = 1,NSTEPS,INCX
W = SX(I)
Z = SY(I)
SX(I) = W*SH11 + Z*SH12
SY(I) = W*SH21 + Z*SH22
END DO
ELSE IF (SFLAG.EQ.ZERO) THEN
SH12 = SPARAM(4)
SH21 = SPARAM(3)
DO I = 1,NSTEPS,INCX
W = SX(I)
Z = SY(I)
SX(I) = W + Z*SH12
SY(I) = W*SH21 + Z
END DO
ELSE
SH11 = SPARAM(2)
SH22 = SPARAM(5)
DO I = 1,NSTEPS,INCX
W = SX(I)
Z = SY(I)
SX(I) = W*SH11 + Z
SY(I) = -W + SH22*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 (SFLAG.LT.ZERO) THEN
SH11 = SPARAM(2)
SH12 = SPARAM(4)
SH21 = SPARAM(3)
SH22 = SPARAM(5)
DO I = 1,N
W = SX(KX)
Z = SY(KY)
SX(KX) = W*SH11 + Z*SH12
SY(KY) = W*SH21 + Z*SH22
KX = KX + INCX
KY = KY + INCY
END DO
ELSE IF (SFLAG.EQ.ZERO) THEN
SH12 = SPARAM(4)
SH21 = SPARAM(3)
DO I = 1,N
W = SX(KX)
Z = SY(KY)
SX(KX) = W + Z*SH12
SY(KY) = W*SH21 + Z
KX = KX + INCX
KY = KY + INCY
END DO
ELSE
SH11 = SPARAM(2)
SH22 = SPARAM(5)
DO I = 1,N
W = SX(KX)
Z = SY(KY)
SX(KX) = W*SH11 + Z
SY(KY) = -W + SH22*Z
KX = KX + INCX
KY = KY + INCY
END DO
END IF
END IF
RETURN
END
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