Four-point one-sided second-derivative formula
= Four-point one-sided second-derivative formula
At unit spacing, exactness through cubic polynomials gives
$$
f''(-1)\approx2f(-1)-5f(0)+4f(1)-f(2).
$$
= Four-point one-sided second-derivative formula
At unit spacing, exactness through cubic polynomials gives
$$
f''(-1)\approx2f(-1)-5f(0)+4f(1)-f(2).
$$