11.4 3 parameters fit

\[ \frac{k}{m} \cot{ \delta}=\frac{1}{am}+\frac{r_0 m }{2}\frac{k^2}{m^2}+ \frac{P_2 r_0^3 k^4}{m} \]

\(P[0]=am\) , \(P[1]=r_0m\) , \(P[2]=P_2\)

\[\begin{gather} \chi^2/d.o.f.=5.58424 \\ P[0]=-0.120224\pm (0.0028) \\ P[1]=-17.0848\pm (0.64) \\ P[2]=-0.000368459\pm (3.7e-06) \\ \end{gather}\] {\[\begin{gather} C=\begin{pmatrix} 8.03e-06& -0.282& -0.283\\ -0.282& 0.413& 0.743\\ -0.283& 0.743& 1.35e-11\\ \end{pmatrix} \end{gather}\]}