Parametric representations of neutron-star equations of state with phase transitions

This paper explores the use of low-dimensional parametric representations of neutron-star equations of state that include discontinuities caused by phase transitions. The accuracies of optimal piecewise-analytic and spectral representations are evaluated for equations of state having first- or second-order phase transitions with a wide range of discontinuity sizes. These results suggest that the piecewise-analytic representations of these nonsmooth equations of state are convergent, while the spectral representations are not. Nevertheless, the lower-order ($2\ensuremath{\le}{N}_{\text{parms}}\ensuremath{\le}7$) spectral representations are found to be more accurate than the piecewise-analytic representations with the same number of parameters.