creating constraint with in between two same variables

[r.ilma...@gmail.com]

Dear all,

I'd like to build a constraint as such:

model.y[i] * 0.98 <= demand <= model.y[i] 

in Pyomo, however it gave error. I tried the following:

    def service_rule (model,i):

        return  sum(model.arrival [o,d,veh] * model.lam[i,o,d,veh]  for o,d,veh in model.q) <= model.y_pc[i]

    model.service = Constraint(model.Nodes, rule = service_rule)

    def minimum_charger_rule (model, i):

        return  model.y_pc[i]*0.98 <=sum(model.arrival [o,d,veh] * model.lam[i,o,d,veh]  for o,d,veh in model.q)

   

    model.min_charge = Constraint(model.Nodes, rule = minimum_charger_rule)

However, it gave error in large model due to computational limitation. Does anybody have a suggestion in formulating this?

Thank you in advance