mat_rswap Subroutine

subroutine mat_rswap(n,x,incx,y,incy)
integer         :: n
doubleprecision :: x(*)
integer         :: incx
doubleprecision :: y(*)
integer         :: incy

doubleprecision :: t
integer         :: ix
integer         :: iy
integer         :: i

   if (n .le. 0) return
   ix = 1
   iy = 1
   if (incx.lt.0) ix = (-n+1)*incx+1
   if (incy.lt.0) iy = (-n+1)*incy+1
   do i = 1, n
      t = x(ix)
      x(ix) = y(iy)
      y(iy) = t
      ix = ix + incx
      iy = iy + incy
   enddo
end subroutine mat_rswap