subroutine  zswap (n,zx,incx,zy,incy)
c
c     interchanges two vectors.
c     jack dongarra, 3/11/78.
c
      double complex zx(1),zy(1),ztemp
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
        ztemp = zx(ix)
        zx(ix) = zy(iy)
        zy(iy) = ztemp
        ix = ix + incx
        iy = iy + incy
   10 continue
      return
c
c       code for both increments equal to 1
   20 do 30 i = 1,n
        ztemp = zx(i)
        zx(i) = zy(i)
        zy(i) = ztemp
   30 continue
      return
      end