Likelihood-free methods perform parameter inference in stochastic simulator
models where evaluating the likelihood is intractable but sampling synthetic
data is possible. One class of methods for this likelihood-free problem uses a
classifier to distinguish between pairs of parameter-observation samples
generated using the simulator and pairs sampled from some reference
distribution, which implicitly learns a density ratio proportional to the
likelihood. Another popular class of methods fits a conditional distribution to
the parameter posterior directly, and a particular recent variant allows for
the use of flexible neural density estimators for this task. In this work, we
show that both of these approaches can be unified under a general contrastive
learning scheme, and clarify how they should be run and compared.

该研究探讨了两种不需要概率似然函数的方法来处理具有随机模拟器模型的参数推断问题，分别是通过分类器学习隐含的密度比例和构建条件分布进行参数后验的灵活神经密度估计。研究表明这两种方法可以共同运行于一种对比学习策略下，并详细解释了它们如何运行和相互比较。