# Structure Coefficients¶

The structure coefficients for composite polytropic models are evaluated using

$\begin{split}\begin{gather} V_{2} = -(n_{i} + 1) \frac{z_{\rm s}^{2}}{z} \frac{\theta'_{i}}{\theta_{i}}, \qquad \As = V_{2} \frac{z^{2}}{z_{\rm s}^{2}}\left( \frac{n_{i}}{n_{i} + 1} - \frac{1}{\Gamma_{1}} \right), \\ U = \frac{t_{i} z^{3}}{\mu_{i}} \theta_{i}^{n_{i}}, \qquad c_1 = \frac{z^{3}}{z_{\rm s}^{3}} \frac{\mu_{\rm s}}{\mu_{i}}, \end{gather}\end{split}$

where $$\mu$$ is the auxiliary mass variable introduced above.