SUBROUTINE  DROT (N,DX,INCX,DY,INCY,C,S)

C     APPLIES A PLANE ROTATION.
C     JACK DONGARRA, LINPACK, 3/11/78.

      DOUBLE PRECISION DX(*),DY(*),DTEMP,C,S
      INTEGER I,INCX,INCY,IX,IY,N

      IF(N.LE.0)RETURN
      IF(INCX.EQ.1.AND.INCY.EQ.1)GO TO 20

C       CODE FOR UNEQUAL INCREMENTS OR EQUAL INCREMENTS NOT EQUAL
C         TO 1

      IX = 1
      IY = 1
      IF(INCX.LT.0)IX = (-N+1)*INCX + 1
      IF(INCY.LT.0)IY = (-N+1)*INCY + 1
      DO 10 I = 1,N
        DTEMP = C*DX(IX) + S*DY(IY)
        DY(IY) = C*DY(IY) - S*DX(IX)
        DX(IX) = DTEMP
        IX = IX + INCX
        IY = IY + INCY
   10 CONTINUE
      RETURN

C       CODE FOR BOTH INCREMENTS EQUAL TO 1

   20 DO 30 I = 1,N
        DTEMP = C*DX(I) + S*DY(I)
        DY(I) = C*DY(I) - S*DX(I)
        DX(I) = DTEMP
   30 CONTINUE
      RETURN
      END