srotm.f

          SUBROUTINE SROTM(N,SX,INCX,SY,INCY,SPARAM)
    *     .. Scalar Arguments ..
          INTEGER INCX,INCY,N
    *     ..
    *     .. Array Arguments ..
          REAL SPARAM(5),SX(1),SY(1)
    *     ..
    *
    *  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
    *     (DX**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 5 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)) GO TO 140
          IF (.NOT. (INCX.EQ.INCY.AND.INCX.GT.0)) GO TO 70
    *
          NSTEPS = N*INCX
          IF (SFLAG) 50,10,30
       10 CONTINUE
          SH12 = SPARAM(4)
          SH21 = SPARAM(3)
          DO 20 I = 1,NSTEPS,INCX
              W = SX(I)
              Z = SY(I)
              SX(I) = W + Z*SH12
              SY(I) = W*SH21 + Z
       20 CONTINUE
          GO TO 140
       30 CONTINUE
          SH11 = SPARAM(2)
          SH22 = SPARAM(5)
          DO 40 I = 1,NSTEPS,INCX
              W = SX(I)
              Z = SY(I)
              SX(I) = W*SH11 + Z
              SY(I) = -W + SH22*Z
       40 CONTINUE
          GO TO 140
       50 CONTINUE
          SH11 = SPARAM(2)
          SH12 = SPARAM(4)
          SH21 = SPARAM(3)
          SH22 = SPARAM(5)
          DO 60 I = 1,NSTEPS,INCX
              W = SX(I)
              Z = SY(I)
              SX(I) = W*SH11 + Z*SH12
              SY(I) = W*SH21 + Z*SH22
       60 CONTINUE
          GO TO 140
       70 CONTINUE
          KX = 1
          KY = 1
          IF (INCX.LT.0) KX = 1 + (1-N)*INCX
          IF (INCY.LT.0) KY = 1 + (1-N)*INCY
    *
          IF (SFLAG) 120,80,100
       80 CONTINUE
          SH12 = SPARAM(4)
          SH21 = SPARAM(3)
          DO 90 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
       90 CONTINUE
          GO TO 140
      100 CONTINUE
          SH11 = SPARAM(2)
          SH22 = SPARAM(5)
          DO 110 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
      110 CONTINUE
          GO TO 140
      120 CONTINUE
          SH11 = SPARAM(2)
          SH12 = SPARAM(4)
          SH21 = SPARAM(3)
          SH22 = SPARAM(5)
          DO 130 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
      130 CONTINUE
      140 CONTINUE
          RETURN
          END