[R-SIG-Finance] Mixed integer programming

[Hannu Kahra]

I have tried to replicate Example 5.1 in Luenberger: Investment Science.

Here is the model
model <- MIPModel() %>%
  add_variable(x[i], i = 1:7, type = "binary") %>%
  set_objective(200*x[1]+30*x[2]+200*x[3]+60*x[4]+50*x[5]+100*x[6]+50*x[7])
%>%

add_constraint(100*x[1]+20*x[2]+150*x[3]+50*x[4]+50*x[5]+150*x[6]+150*x[7]
<= 500)
solve_model(with_ROI("glpk",verbose = TRUE))

I get the following error

Error in UseMethod("solve_model") :
  no applicable method for 'solve_model' applied to an object of class
"function"

 modelMixed integer linear optimization problem
Variables:
  Continuous: 0
  Integer: 0
  Binary: 7
Model sense: maximize
Constraints: 1

What is wrong? Thank you in advance.

-Hannu

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