Registering doRNG for Persistent Reproducible Parallel Foreach Loops

Description

registerDoRNG registers the doRNG foreach backend. Subsequent %dopar% loops are then performed using the previously registered foreach backend, but are internally performed as %dorng% loops, making them fully reproducible.

Usage

registerDoRNG(seed = NULL, once = TRUE)

Arguments

seed
a numerical seed to use (as a single or 6-length numerical value)
once
a logical to indicate if the RNG sequence should be seeded at the beginning of each loop or only at the first loop.

Details

Briefly, the RNG is set, before each iteration, with seeds for L'Ecuyer's CMRG that overall generate a reproducible sequence of statistically independent random streams.

Note that (re-)registering a foreach backend other than doRNG, after a call to registerDoRNG disables doRNG -- which then needs to be registered.

Examples



library(doParallel)
cl <- makeCluster(2)
registerDoParallel(cl)

# One can make reproducible loops using the %dorng% operator
r1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
# or convert %dopar% loops using registerDoRNG
registerDoRNG(1234)
r2 <- foreach(i=1:4) %dopar% { runif(1) }
identical(r1, r2)

## [1] TRUE

stopCluster(cl)

# Registering another foreach backend disables doRNG
cl <- makeCluster(2)
registerDoParallel(cl)
set.seed(1234)
s1 <- foreach(i=1:4) %dopar% { runif(1) }
set.seed(1234)
s2 <- foreach(i=1:4) %dopar% { runif(1) }
identical(s1, s2)

## [1] FALSE



# doRNG is re-nabled by re-registering it
registerDoRNG()
set.seed(1234)
r3 <- foreach(i=1:4) %dopar% { runif(1) }
identical(r2, r3)

## [1] TRUE

# NB: the results are identical independently of the task scheduling
# (r2 used 2 nodes, while r3 used 3 nodes)

# argument `once=FALSE` reseeds doRNG's seed at the beginning of each loop
registerDoRNG(1234, once=FALSE)
r1 <- foreach(i=1:4) %dopar% { runif(1) }
r2 <- foreach(i=1:4) %dopar% { runif(1) }
identical(r1, r2)

## [1] TRUE

# Once doRNG is registered the seed can also be passed as an option to %dopar%
r1.2 <- foreach(i=1:4, .options.RNG=456) %dopar% { runif(1) }
r2.2 <- foreach(i=1:4, .options.RNG=456) %dopar% { runif(1) }
identical(r1.2, r2.2) && !identical(r1.2, r1)

## [1] TRUE



stopCluster(cl)

See also

%dorng%