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Callback Parameter

Source: R/029_expressions_constants_callback_param.R
CallbackParam.Rd

A Parameter whose value is computed by a user-supplied callback function rather than stored explicitly. Mirrors CVXPY's cp.CallbackParam (cvxpy/expressions/constants/callback_param.py).

Usage

CallbackParam(
  callback,
  shape = c(1L, 1L),
  name = NULL,
  id = NULL,
  latex_name = NULL,
  ...
)

Arguments

callback

A function (no arguments) returning the parameter's numeric value. Re-evaluated on every read of value(param).

shape

Integer vector of length 1 or 2 giving parameter dimensions. Defaults to c(1, 1) (scalar).

name

Optional character string name.

id

Optional integer ID. If NULL, a unique ID is generated.

latex_name

Optional LaTeX name for visualisation.

...

Other Parameter attributes (e.g., nonneg, nonpos).

Value

A CallbackParam object (subclass of Parameter).

Details

Each call to value(param) re-evaluates the callback and validates the returned numeric against the parameter's shape and attribute domain. Setting via value(param) <- v is not allowed and signals an error.

DPP use

If p and q are scalar Parameters, the expression p * q is not DPP. Wrapping it in a CallbackParam,


pq <- CallbackParam(callback = function() value(p) * value(q))

yields a DPP-compliant Parameter whose value tracks p and q automatically.

Examples

p <- Parameter(); value(p) <- 2
q <- Parameter(); value(q) <- 3
pq <- CallbackParam(callback = function() value(p) * value(q))
value(pq)   # evaluates the callback => 6
#>      [,1]
#> [1,]    6