“…On the other hand, methods to approximate the true posterior pdf mainly include Markov Chain Monte Carlo (MCMC), variational Bayes and ensemble-based methods (e.g. ensemble Kalman filter and ensemble smoother) (Olalotiti-Lawal and Datta-Gupta, 2018;Emerick and Reynolds, 2013;Song et al, 2021;Povala et al, 2022). These methods approximate the posterior pdf using sample distributions, in the case of MCMC and ensemble-based methods, or trial functions in the case of variational Bayes.…”