Does an expression vary across scenarios?

An expression that contains a random variable has a different value in each scenario, and is called random. Summarizing it across the scenarios, for example with expectation(), gives a single number again: demand - stock is random, expectation(demand - stock) is not, and neither is 3 * stock.

Usage

is_random(x)

Arguments

x

An expression, or a numeric vector (which is never random).

Value

A logical vector with one element per element of x.

Details

An objective or a constraint must not be random, and a summary such as expectation() needs a random expression to summarize. quicopt checks both rules itself and stops with an error when one is broken, so you need is_random() only in your own code, for example in a function that accepts both kinds of expression.

Examples

m <- model()
stock  <- num_var(m, "stock", lower = 0, upper = 200)
demand <- rand_var(m, "demand", normal(100, 15))
is_random(demand - stock)                  # TRUE
#> [1] TRUE
is_random(expectation(demand - stock))     # FALSE
#> [1] FALSE
is_random(c(stock, stock^2))               # FALSE FALSE
#> [1] FALSE FALSE