The earliest phase of an ultrarelativistic heavy-ion collision can be described as a highly populated system of gluons called glasma. The system's dynamics is governed by the classical Yang-Mills equation. Solutions can be found at early times using a proper time expansion. Since the expansion parameter is the proper time, this method is necessarily limited to the study of early time dynamics. In addition compute time and memory limitations restrict practical calculations to no more than eighth order in the expansion. The result is that the method produces reliable results only for very early times. In this paper we explore three different methods to increase the maximum time that can be reached. We use Padé approximants to extrapolate analytic results calculated previously at eighth order in the proper time expansion M. E. Carrington et al. [Phys. Rev. C 108, 054903 (2023)]. We also use an analytic approximation based on the assumption that there are two widely separated ultraviolet scales M. Li et al. [Phys. Rev. C 94, 024908 (2016)] to extend the proper time expansion to 20th order. Lastly, we develop a machine learning method to learn an expression for the transverse-longitudinal pressure anisotropy using symbolic regression. We find that, depending slightly on the quantity being calculated, the latest time for which reliable results are obtained can be extended approximately 1.5 times (from $\sim 0.05 \mathrm{fm}/c$ using previous methods to about 0.08 $\mathrm{fm}/c$).

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• Relativistic heavy-ion collisions