subroutine  cswap (n,cx,incx,cy,incy)
c
c     interchanges two vectors.
c     jack dongarra, linpack, 3/11/78.
c     modified 12/3/93, array(1) declarations changed to array(*)
c
      complex cx(*),cy(*),ctemp
      integer i,incx,incy,ix,iy,n
c
      if(n.le.0)return
      if(incx.eq.1.and.incy.eq.1)go to 20
c
c       code for unequal increments or equal increments not equal
c         to 1
c
      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
        ctemp = cx(ix)
        cx(ix) = cy(iy)
        cy(iy) = ctemp
        ix = ix + incx
        iy = iy + incy
   10 continue
      return
c
c       code for both increments equal to 1
   20 do 30 i = 1,n
        ctemp = cx(i)
        cx(i) = cy(i)
        cy(i) = ctemp
   30 continue
      return
      end