我在代码中看到了诸如之类的离散化代码，( ) 尝试$\frac{d^2T(x)}{d^2x}$$x = sin(\theta)$

   !============== here are some defined variables
   deltaTheta = pi/150
   deltax(i) = cos(theta(i)) * deltaTheta  
   dx = 0.5*(deltax(i) + deltax(i+1))
   dx1 = 0.5*(deltax(i-1)+ deltax(i))
   !============== here is the discretization that I am talking about
   ... = ((T(i+1) - T(i))/dx - (T(i) - T(i-1))/dx1)/(0.5 *(dx + dx1))

这种离散化是针对非边界城市的；这种离散化叫什么？