Good morning.

I need to approximate the second derivative for a discrete function with only few points. My first intuition was to use the traditionnal formula:
[approximation of the second derivative](https://i.stack.imgur.com/i6Pnd.png)

Unfortunately my available points are not at symmetrical distance from to the other. In consequence I have clearly doubtful results, with positivesecond derivative while my function is concave.

My question is, do have I to modify the coefficients in my formula to take into account the asymmetry between my two points ? And if I have to do so, which weights to use ?
If my intuition is false, what would you recommend to me to do to take into account the assymetry ?

Thank you very much