Optimization with ompr


I want to add a new constraint to my optimization model. I work with ompr library. I have stores (j) and customers (i). I want to minimize transportation cost.

My model:

MIPModel() %>%
  # 1 iff i gets assigned to warehouse j
  add_variable(x[i, j], i = 1:n, j = 1:m, type = "binary") %>%
  # 1 iff warehouse j is built
  add_variable(y[j], j = 1:m, type = "binary") %>%
  # maximize the preferences
  set_objective(sum_expr(transportcost(i, j) * x[i, j], i = 1:n, j = 1:m) + 
                  sum_expr(fixedcost[j] * y[j], j = 1:m), "min") %>%
  # every customer needs to be assigned to a warehouse
  add_constraint(sum_expr(x[i, j], j = 1:m) == 1, i = 1:n) %>% 
  # if a customer is assigned to a warehouse, then this warehouse must be built
  add_constraint(x[i,j] <= y[j], i = 1:n, j = 1:m)

I want to add a new constraint. For example I have 30 different stores. First 10 stores have to sell minimum 15 units, second 20 stores have to sell minimum 10 units and third 30 stores have to sell 5 units.

I try to write like this but it didn't work:

  add_constraint(sum_expr(x[i, j], j = 1:10) >= 15, i = 1:n) 

Thank you!!

I believe you may be asking for help with ompr (I can't find omprt).
Recommend you adjust your title if this is the case

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