“…The first category includes the Tikhonov regularization (Skaggs & Kabala 1994), nonlinear optimization with embedding (Mahar & Datta 1997), non-regularized nonlinear least squares (Alapati & Kabala 2000), progressive genetic algorithms (Aral et al 2001), a constrained robust least squares (Sun et al 2006) and heuristic harmony search algorithms (Ayvaz 2010). The second category adopts probability-based methods: statistical pattern recognition (Datta et al 1989); minimum relative entropy (Woodbury & Ulrych 1996, Woodbury et al 1998; geostatistical approaches (Snodgrass & Kitanidis 1997, Michalak & Kitanidis 2004a,b, Neupauer et al 2000, Butera & Tanda 2003, Butera et al 2006, Gzyl et al 2014; empirical Bayesian methods combined with Akaike's Bayesian Information Criterion (Zanini & Woodbury 2016); Bayesian global optimization (Pirot et al 2019) and ensemble Kalman filter methods (Xu & Gómez-Hernández 2016, 2018, Chen et al 2018, Xu et al 2020).…”