run_camodel {chouca}R Documentation

Run a cellular automata

Description

Run a pre-defined stochastic cellular automaton

Usage

run_camodel(mod, initmat, times, control = list())

Arguments

mod

A stochastic cellular automaton model defined using camodel

initmat

An initial matrix to use for the simulation, possibly created using generate_initmat

times

A numeric vector describing the time sequence for which output is wanted. Time will always start at zero but output will only be saved at the time steps specified in this vector.

control

a named list with settings to alter the way the simulation is run (see full list of settings in 'Details' section)

Details

run_camodel() is the workhorse function to run cellular automata. It runs the simulation and outputs the results at the time steps specified by the times argument, starting from the initial landscape initmat (a matrix typically created by generate_initmat).

Note that the simulation is run for all time steps, but output is only provided for the time steps specified in times.

The control list must have named elements, and allows altering the way the simulation is run, including the live display of covers or landscapes (see trace_plotter or landscape_plotter).

Possible options are the following:

  1. save_covers_every By default, global covers are saved for each time step specified in times. Setting this argument to values higher than one will skip some time steps (thinning). For example, setting it to 2 will make run_camodel save covers only every two values specified in times. Set to 0 to skip saving covers. This value must be an integer.

  2. save_snapshots_every In the same way as covers, landscape snapshots can be saved every set number of values in times. By default, only the initial and final landscape are saved. Set to one to save the landscape for each value specified in times. Higher values will skip elements in times by the set number. Set to zero to turn off the saving of snapshots. This value must be an integer.

  3. console_output_every Set the number of iterations between which progress report is printed on the console. Set to zero to turn off progress report. The default option is to print progress five times during the simulation.

  4. custom_output_fun A custom function can be passed using this argument to compute something on the landscape as the simulation is being run. This function can return anything, but needs to take two arguments, the first one being the current time in the simulation (single numeric value), and the other one the current landscape (a matrix). This can be used to plot the simulation results as it is being run, see landscape_plotter and trace_plotter for such use case.

  5. custom_output_every If custom_output_fun is specified, then it will be called for every time step specified in the times vector. Increase this value to skip some time points, in a similar way to covers and snapshots above.

  6. substeps Stochastic CA can run into issues where the probabilities of transitions are above one. A possible solution to this is to run the model in 'substeps', i.e. an iteration is divided in several substeps, and the substeps are run subsequently with probabilities divided by this amount. For example, a model run with 4 substeps means that each iteration will be divided in 4 'sub-iterations', and probabilities of transitions are divided by 4 for each of those sub-iterations.

  7. engine The engine used to run the simulations. Accepted values are 'cpp' to use the C++ engine, or 'compiled', to emit and compile the model code on the fly. Default is to use the C++ engine. Note that the 'compiled' engine uses its own random number generator, and for this reason may produce simulations that are different from the C++ engine (it does respect the R seed however). You will need a compiler to use the 'compiled' engine, which may require you to install Rtools on Windows systems.

  8. precompute_probas (Compiled engine only) Set to TRUE to precompute probabilities of transitions for all possible combinations of neighborhood. When working with a model with a low number of states (typically 3 or 4), this can increase simulation speed dramatically. By default, a heuristic is used to decide whether to enable precomputation or not.

  9. verbose_compilation (Compiled engine only) Set to TRUE to print Rcpp messages when compiling the model. Default is FALSE.

  10. force_compilation (Compiled engine only) chouca has a cache system to avoid recompiling similar models. Set this argument to TRUE to force compilation every time the model is run.

  11. write_source (Compiled engine only) A file name to which the C++ code used to run the model will be written (mostly for debugging purposes).

  12. cores (Compiled engine only) The number of threads to use to run the model. This provides a moderate speedup in most cases, and is sometimes counter-productive on small landscapes. If you plan on running multiple simulations, you are probably better off parallelizing at a higher level. See also the 'Performance' section in the vignette, accessible using the command vignette("chouca-package").

Value

A ca_model_result objects, which is a list with the following components:

  1. model The original model used for the model run (see return value of camodel for more details about these objects).

  2. initmat The initial landscape (matrix) used for the model run, such as what is returned by generate_initmat.

  3. times The time points vector at which output is saved

  4. control The control list used for the model run, containing the options used for the run

  5. output A named list containing the simulation outputs. The 'covers' component contains a matrix with the first column containing the time step, and the other columns the proportions of cells in a given state. The 'snapshots' component contains the landscapes recorded as matrices(camodel_initmat objects), with a 't' attribute indicating the corresponding time step of the model run. The 'custom' component contains the results from calling a custom function provided as 'custom_output_fun' in the control list (see examples below).

See Also

camodel, generate_initmat, trace_plotter, landscape_plotter, run_meanfield

Examples


# Run a model with default parameters
mod <- ca_library("musselbed")
im  <- generate_initmat(mod, c(0.4, 0.6, 0), nrow = 100, ncol = 50)
out <- run_camodel(mod, im, times = seq(0, 100))
plot(out)

# Disable console output 
opts <- list(console_output_every = 0) 
out <- run_camodel(mod, im, times = seq(0, 100), control = opts)

# 



# Run the same model with the 'compiled' engine, and save snapshots. This
# requires a compiler on your computer (typically available by installing
# 'Rtools' on Windows)
ctrl <- list(engine = "compiled", save_covers_every = 1, save_snapshots_every = 100)
run <- run_camodel(mod, im, times = seq(0, 100), control = ctrl)
plot(run)

# 
oldpar <- par(mfrow = c(1, 2))
image(run, snapshot_time = 0)
image(run, snapshot_time = 100)
par(oldpar)

# Disable console output
ctrl <- list(console_output_every = 0)
run <- run_camodel(mod, im, times = seq(0, 100), control = ctrl)
plot(run)

# Very verbose console output (display compilation information, etc.)
ctrl <- list(console_output_every = 1,
             verbose_compilation = TRUE,
             engine = "compiled",
             force_compilation = TRUE)
run <- run_camodel(mod, im, times = seq(0, 100), control = ctrl)

# Turn on or off the memoisation of transition probabilities (mind the speed
# difference)
ctrl <- list(engine = "compiled", precompute_probas = FALSE)
run <- run_camodel(mod, im, times = seq(0, 256), control = ctrl)
ctrl2 <- list(engine = "compiled", precompute_probas = TRUE)
run2 <- run_camodel(mod, im, times = seq(0, 256), control = ctrl2)

# Use a custom function to compute statistics while the simulation is running
fun <- function(t, mat) {
  # Disturbed cell to mussel cell ratio
  ratio <- mean(mat == "DISTURB") / mean(mat == "MUSSEL")
  data.frame(t = t, ratio = ratio)
}
ctrl <- list(custom_output_fun = fun, custom_output_every = 1)

run <- run_camodel(mod, im, times = seq(0, 256), control = ctrl)
stats <- do.call(rbind, run[["output"]][["custom"]])
plot(stats[ ,1], stats[ ,2], ylab = "DISTURB/MUSSEL ratio", xlab = "time", type = "l")
[Package chouca version 0.1.99 Index]