15.4 fitting the energy levels

We minimise the $\chi^2$ $$\chi^2= \sum_i \frac{( \Delta E_2^{predicted} -\Delta E_2^{latt})^2}{\sigma^2}$$

$$\begin{gather} \chi^2/d.o.f.=2.85717 \\ P[0]=-0.153314\pm (0.0012) \\ P[1]=-3.07443\pm (0.12) \\ \end{gather}$$ { $$\begin{gather} C=\begin{pmatrix} 1.51e-06& 0.669\\ 0.669& 0.0134\\ \end{pmatrix} \end{gather}$$ }