v1.5.4

• support Matern covariance functions with general shape parameters (‘cov_fct_shape’), not just 0.5, 1.5, 2.5
• reduce memory footprint of ‘vecchia’ approximation
• "make 'fitc' and 'full_scale_taperig' approximations numerically more stable
• [python-package] add function ‘tune_pars_TPE_algorithm_optuna’ for choosing tuning parameters with the Tree-structured Parzen estimator algorithm
• [R-package] add function ‘tune.pars.bayesian.optimization’ for choosing tuning parameters using Bayesian optimization and the ‘mlrMBO’ R package
• change default initial values for marginal variances when having multiple random effects
• [R-package] fix bug in ‘gpb.grid.search.tune.parameters’ for ‘metric’ parameter for metrics for which higher is better (auc, average_precision)
• other bug fixes