integer :: i,j
integer, parameter :: nx=10, ny=10
real, dimension(-nx:nx, -ny:ny) :: u,v,w
real, parameter :: h

do i=-nx,nx
do j=-ny,ny

   v = (u(i+1,j)-u(i-1,j))/(2*h)
   w = (u(i,j+1)-u(i,j-1))/(2*h)

end do
end do