fix issues #1373 and #1378

DESCRIPTION

@@ -2,8 +2,8 @@ Package: brms
 Encoding: UTF-8
 Type: Package
 Title: Bayesian Regression Models using 'Stan'
-Version: 2.17.5
-Date: 2022-06-02
+Version: 2.17.6
+Date: 2022-08-12
 Authors@R:
     c(person("Paul-Christian", "Bürkner", email = "paul.buerkner@gmail.com",
              role = c("aut", "cre")),

NEWS.md

@@ -4,6 +4,8 @@
 
 * Support regression splines with fixed degrees of freedom 
 specified via `s(..., fx = TRUE)`.
+* Reuse user-specified control arguments originally passed 
+to the Stan backend in `update` and related methods. (#1373, #1378)
 
 ### Bug Fixes
 

R/brm.R

@@ -538,7 +538,8 @@ brm <- function(formula, data, family = gaussian(), prior = NULL,
       formula = formula, data = data, data2 = data2, prior = prior,
       stanvars = stanvars, model = model, algorithm = algorithm,
       backend = backend, threads = threads, opencl = opencl,
-      save_pars = save_pars, ranef = ranef, family = family
+      save_pars = save_pars, ranef = ranef, family = family,
+      stan_args = list(...)
     )
     exclude <- exclude_pars(x)
     # generate Stan data before compiling the model to avoid

R/brmsfit-class.R

@@ -26,6 +26,8 @@
 #' @slot threads An object of class `brmsthreads` created by
 #'   \code{\link{threading}}.
 #' @slot opencl An object of class `brmsopencl` created by \code{\link{opencl}}.
+#' @slot stan_args Named list of additional control arguments that were passed
+#'   to the Stan backend directly.
 #' @slot fit An object of class \code{\link[rstan:stanfit-class]{stanfit}}
 #'   among others containing the posterior draws.
 #' @slot criteria An empty \code{list} for adding model fit criteria
@@ -56,7 +58,7 @@ brmsfit <- function(formula = NULL, data = data.frame(), prior = empty_prior(),
                     ranef = empty_ranef(), save_pars = NULL,
                     algorithm = "sampling", backend = "rstan",
                     threads = threading(), opencl = opencl(),
-                    fit = NULL, criteria = list(),
+                    stan_args = list(), fit = NULL, criteria = list(),
                     file = NULL, family = NULL, autocor = NULL,
                     cov_ranef = NULL, stan_funs = NULL, data.name = "") {
   version <- list(
@@ -71,8 +73,8 @@ brmsfit <- function(formula = NULL, data = data.frame(), prior = empty_prior(),
   }
   x <- nlist(
     formula, data, prior, data2, stanvars, model, ranef,
-    save_pars, algorithm, backend, threads, opencl, fit, criteria, file,
-    version, family, autocor, cov_ranef, stan_funs, data.name
+    save_pars, algorithm, backend, threads, opencl, stan_args, fit, criteria,
+    file, version, family, autocor, cov_ranef, stan_funs, data.name
   )
   class(x) <- "brmsfit"
   x

R/restructure.R

@@ -216,14 +216,19 @@ restructure_v2 <- function(x) {
       # should always have exactly one row but still check whether it has
       # any rows at all to prevent things from breaking accidentally
       if (NROW(prior_sub_i)) {
-        x$prior[i, c("lb", "ub")] <- prior_sub_i[1, c("lb", "ub")] 
+        x$prior[i, c("lb", "ub")] <- prior_sub_i[1, c("lb", "ub")]
       } else {
         x$prior[i, c("lb", "ub")] <- ""
       }
     }
     x$prior$lb[is.na(x$prior$lb)] <- x$prior$ub[is.na(x$prior$ub)] <- ""
     x$prior <- move2end(x$prior, "source")
   }
+  if (version < "2.17.6") {
+    # a slot was added that stores additional control arguments
+    # that are directly passed to the Stan backends for later reuse #1373
+    x$stan_args <- list()
+  }
   x
 }
 

R/update.R

@@ -202,6 +202,9 @@ update.brmsfit <- function(object, formula., newdata = NULL,
     control <- attr(object$fit@sim$samples[[1]], "args")$control
     control <- control[setdiff(names(control), names(dots$control))]
     dots$control[names(control)] <- control
+    # reuse backend arguments originally passed to brm via ... #1373
+    names_old_stan_args <- setdiff(names(object$stan_args), names(dots))
+    dots[names_old_stan_args] <- object$stan_args[names_old_stan_args]
   }
 
   if (is.null(recompile)) {