```
#' An S3 class to represent a Variable.
#'
#' This is class should only directly be used if you develop your own solver.
#'
#' @param arity the number of subscripts the variable has
#' @param type the type of the variable must be one of
#' (binary, continuous, integer). Default is continuous.
#' @param lb an optional lower bound. No value means unbounded.
#' @param ub an optional upper bound. No value means unbounded.
#' @param instances a character vector with an entry for each
#' variable instance.
#'
#' @noRd
new_variable <- function(arity, type, instances, lb, ub,
variable_expression, variable_quantifiers) {
stopifnot(length(arity) == 1)
stopifnot(length(type) == 1)
stopifnot(arity >= 0)
stopifnot(type %in% c("binary", "continuous", "integer"))
structure(list(arity = arity,
type = type, instances = instances,
lb = lb, ub = ub),
class = "model_variable")
}
```

Embedding an R snippet on your website

Add the following code to your website.

For more information on customizing the embed code, read Embedding Snippets.