Machine-guided Exploration and Calibration of Astrophysical Simulations
  We apply a novel method with machine learning to calibrate sub-grid models
within numerical simulation codes to achieve convergence with observations and
between different codes. It utilizes active learning and neural density
estimators. The hyper parameters of the machine are calibrated with a
well-defined projectile motion problem. Then, using a set of 22 cosmological
zoom simulations, we tune the parameters of a popular star formation and
feedback model within Enzo to match simulations. The parameters that are
adjusted include the star formation efficiency, coupling of thermal energy from
stellar feedback, and volume into which the energy is deposited. This number
translates to a factor of more than three improvements over manual calibration.
Despite using fewer simulations, we obtain a better agreement to the observed
baryon makeup of a Milky-Way (MW) sized halo. Switching to a different
strategy, we improve the consistency of the recommended parameters from the
machine. Given the success of the calibration, we then apply the technique to
reconcile metal transport between grid-based and particle-based simulation
codes using an isolated galaxy. It is an improvement over manual exploration
while hinting at a less known relation between the diffusion coefficient and
the metal mass in the halo region. The exploration and calibration of the
parameters of the sub-grid models with a machine learning approach is concluded
to be versatile and directly applicable to different problems.
