get_param: Get and Set Parameters, Controls, and Initial Conditions in...

In EpiModel: Mathematical Modeling of Infectious Disease Dynamics

Get and Set Parameters, Controls, and Initial Conditions in Network Models

Description

Retrieve, create, and edit the parameters, control settings, and initial conditions of the main netsim_dat object of network models, from inside module functions. They start as the param.net(), control.net(), and init.net() inputs of netsim(), and the three share one set of accessors:

• get_param(), get_control(), and get_init() return one element. get_param_list(), get_control_list(), and get_init_list() return several elements as a named list.

• set_param(), set_control(), and set_init() replace the value of an element, and create the element if it does not exist. add_param(), add_control(), and add_init() create an element set to NA.

• get_network_control() returns the entry for one network layer of a control setting given as a multilayer() object.

Unlike set_attr() and set_epi(), these set_ functions take neither nodes nor a time step: the new value is used from then on, until it is set again.

See net-accessor for an overview of the accessors.

Usage

get_param(dat, item, override.null.error = FALSE)

get_param_list(dat, item = NULL)

set_param(dat, item, value)

add_param(dat, item)

get_control(dat, item, override.null.error = FALSE)

get_control_list(dat, item = NULL)

get_network_control(dat, network, item, override.null.error = FALSE)

set_control(dat, item, value)

add_control(dat, item)

get_init(dat, item, override.null.error = FALSE)

get_init_list(dat, item = NULL)

set_init(dat, item, value)

add_init(dat, item)

Arguments

dat	Main netsim_dat object containing a networkDynamic object and other initialization information passed from netsim().
item	Name of the parameter, control setting, or initial condition. For the ⁠get_*_list()⁠ functions, a character vector of names, or NULL (default) for all elements.
override.null.error	If TRUE, return NULL instead of an error when item does not exist (default = FALSE).
value	New value of the element.
network	Index of the network layer.

Value

For get_param(), get_control(), and get_init(), the value of the element; for get_network_control(), its entry for layer network; for the ⁠get_*_list()⁠ functions, a named list of elements. The other functions return the updated netsim_dat object.

Intended Usage

These accessors operate on the live netsim_dat object that EpiModel constructs internally when a simulation starts and passes through each module at every time step. The expected calling context is inside a user-supplied module function (e.g., a custom infection.FUN, recovery.FUN, or arrivals/departures module) registered with control.net().

They are not a general-purpose tool for editing the user-facing input or output objects of netsim():

• Calling them on a param.net(), init.net(), or control.net() object before a run will appear to succeed (those objects are also list-like) but produces an object that is not a valid simulation input.

• Calling them on the object returned by netsim() modifies only the saved input slot, not anything that would change the result of a re-run. Note also that netsim() strips the ⁠*.FUN⁠ entries from its returned control slot, so feeding that slot back into a new simulation will fail.

For modifications outside a running simulation, use the following instead:

• Editing parameters before a run: update_params() for a param.net object, or direct list assignment (e.g., p$inf.prob <- 0.5).

• Editing init or control before a run: direct list assignment (e.g., ctrl$nsteps <- 1000), or rebuild with a fresh call to the init.net() / control.net() constructor.

• Scheduled mid-simulation changes: the .param.updater.list argument to param.net() and the .control.updater.list argument to control.net(). See the "model-parameters" vignette for the underlying updater module and the scenario API built on top of it.

Mutability

The set_, append_, and add_ functions DO NOT modify the netsim_dat object in place. The result must be assigned back to dat in order to be registered: ⁠dat <- set_*(dat, item, value)⁠.

See Also

net-accessor for an overview of the accessors, and get_attr() and get_epi() for the other groups; update_params() for editing a param.net object outside a simulation.

Examples

dat <- create_dat_object(control = list(nsteps = 150))

dat <- add_param(dat, "x")
get_param(dat, "x")
dat <- set_param(dat, "x", 0.4)
dat <- set_param(dat, "y", 0.8)
get_param_list(dat)
get_param(dat, "x")

# The control and init accessors work the same way
dat <- add_control(dat, "x")
dat <- set_control(dat, "x", 0.4)
get_control_list(dat, c("nsteps", "x"))
get_control(dat, "nsteps")

dat <- add_init(dat, "x")
dat <- set_init(dat, "x", 0.4)
get_init_list(dat)
get_init(dat, "x")

# A control setting with one entry per network layer
dat <- set_control(dat, "z", multilayer(0.1, 0.2))
get_network_control(dat, network = 2, "z")

EpiModel documentation built on Oct. 16, 2026, 5:07 p.m.