chkpt_brms {chkptstanr}

Checkpoint Sampling: brms

Description

Fit Bayesian generalized (non-)linear multivariate multilevel models using brms with checkpointing.

Usage

chkpt_brms(
  formula,
  data,
  iter_warmup = 1000,
  iter_sampling = 1000,
  iter_per_chkpt = 100,
  iter_typical = 150,
  parallel_chains = 2,
  threads_per = 1,
  chkpt_progress = TRUE,
  control = NULL,
  brmsfit = TRUE,
  seed = 1,
  path,
  ...
)

Arguments

formula

An object of class formula, brmsformula, or brms{mvbrmsformula}. Further information can be found in brmsformula.

data

An object of class data.frame (or one that can be coerced to that class) containing data of all variables used in the model.

iter_warmup

(positive integer) The number of warmup iterations to run per chain (defaults to 1000).

iter_sampling

(positive integer) The number of post-warmup iterations to run per chain (defaults to 1000).

iter_per_chkpt

(positive integer). The number of iterations per checkpoint. Note that iter_sampling is divided by iter_per_chkpt to determine the number of checkpoints. This must result in an integer (if not, there will be an error).

iter_typical

(positive integer) The number of iterations in the initial warmup, which finds the so-called typical set. This is an initial phase, and not included in iter_warmup. Note that a large enough value is required to ensure convergence (defaults to 150).

parallel_chains

(positive integer) The maximum number of MCMC chains to run in parallel. If parallel_chains is not specified then the default is to look for the option mc.cores, which can be set for an entire R session by options(mc.cores=value). If the mc.cores option has not been set then the default is 1.

threads_per

(positive integer) Number of threads to use in within-chain parallelization (defaults to 1).

chkpt_progress

logical. Should the chkptstanr progress be printed (defaults to TRUE) ? If set to FALSE, the standard cmdstanr progress bar is printed for each checkpoint (which does not actually keep track of checkpointing progress)

control

A named list of parameters to control the sampler's behavior. It defaults to NULL so all the default values are used. For a comprehensive overview see stan.

brmsfit

Logical. Should a brmsfit object be returned (defaults to TRUE).

seed

(positive integer). The seed for random number generation to make results reproducible.

path

Character string. The path to the folder, that is used for saving the checkpoints.

...

Additional arguments based to make_stancode, including, for example, user-defined prior distributions and the brmsfamily (e.g., family = poisson()).

Value

An object of class brmsfit (with brmsfit = TRUE) or chkpt_brms (with brmsfit = FALSE)

Examples

## Not run: 
library(brms)
library(cmdstanr)

# path for storing checkpoint info
path <- create_folder(folder_name  = "chkpt_folder_fit1")

# "random" intercept
fit1 <- chkpt_brms(bf(formula = count ~ zAge + zBase * Trt + (1|patient),
                      family = poisson()), 
                   data = epilepsy, , 
                   iter_warmup = 1000, 
                   iter_sampling = 1000, 
                   iter_per_chkpt = 250, 
                   path = path)
                   
# brmsfit output
fit1

# path for storing checkpoint info
 path <- create_folder(folder_name  = "chkpt_folder_fit2")

# remove "random" intercept (for model comparison)
fit2 <- chkpt_brms(bf(formula = count ~ zAge + zBase * Trt, 
                      family = poisson()), 
                   data = epilepsy, , 
                   iter_warmup = 1000, 
                   iter_sampling = 1000, 
                   iter_per_chkpt = 250, 
                   path = path)
                   
# brmsfit output
fit2

# compare models
loo(fit1, fit2)


# using custom priors
path <- create_folder(folder_name = "chkpt_folder_fit3")

# priors
bprior <- prior(constant(1), class = "b") +
  prior(constant(2), class = "b", coef = "zBase") +
  prior(constant(0.5), class = "sd")

# fit model
fit3 <-
  chkpt_brms(
    bf(
      formula = count ~ zAge + zBase + (1 | patient),
      family = poisson()
    ),
    data = epilepsy,
    path  = path,
    prior = bprior,
    iter_warmup = 1000,
    iter_sampling = 1000,
    iter_per_chkpt = 250, 
  )


# check priors
prior_summary(fit3)


## End(Not run)