[Optional] Custom policy¶

It is possible to provide a custom policy in policy.h and policy.cpp. We will implement the decision rule as defined in Airplane MDP formulation.

First, we register the policy in mdp.cpp:

void MDP::RegisterPolicies(DynaPlex::Erasure::PolicyRegistry<MDP>& registry) const
{
        registry.Register<RuleBasedPolicy>("rule_based",
                "The heuristic rule");
}

Next, we implement policy.h, we implement the constructor and a function called GetAction(), which takes the state as input and outputs an action. Furthermore, we define several variables that are parameters for tuning the policy.

namespace DynaPlex::Models {
        namespace airplane /*must be consistent everywhere for complete mdp defininition and associated policies.*/
        {
                // Forward declaration
                class MDP;

                class RuleBasedPolicy
                {
                        //this is the MDP defined inside the current namespace!
                        std::shared_ptr<const MDP> mdp;
                        const VarGroup varGroup;
                        double price_threshold_low;
                        double price_threshold_high;
                        int64_t seat_threshold_low;
                        int64_t seat_threshold_high;
                        int64_t remainingday_threshold;
                public:
                        RuleBasedPolicy(std::shared_ptr<const MDP> mdp, const VarGroup& config);
                        int64_t GetAction(const MDP::State& state) const;
                };

        }
}

We can set the parameters in a seperate config file policy_config_0.json:

{
  "id": "rule_based",
  "price_threshold_low": 1000.0,
  "price_threshold_high": 2000.0
}

Next, we implement the policy in policy.cpp:

...
//MDP and State refer to the specific ones defined in current namespace
RuleBasedPolicy::RuleBasedPolicy(std::shared_ptr<const MDP> mdp, const VarGroup& config)
        :mdp{ mdp }
{
        //provide default values and load parameters from json
        config.GetOrDefault("price_threshold_low", price_threshold_low, 0.0);
        config.GetOrDefault("price_threshold_high", price_threshold_high, 1.0);
        //we can also set parameters directly in the constructor
        seat_threshold_low = 1;
        seat_threshold_high = 5;
        remainingday_threshold = 9;
}

int64_t RuleBasedPolicy::GetAction(const MDP::State& state) const
{
        if (state.RemainingSeats > seat_threshold_high)
        {
                return 1;//sell
        }
        if (state.PriceOfferedPerSeat > price_threshold_low)
        {//only sell to type 1 and 2 customers
                if (state.RemainingSeats <= seat_threshold_high && state.RemainingSeats >= seat_threshold_low)
                {
                        if (state.RemainingDays <= remainingday_threshold)
                        {
                                return 1;//sell
                        }

                }
        }
        if (state.PriceOfferedPerSeat > price_threshold_high)
        {//only sell to type 1 customers
                if (state.RemainingSeats <= seat_threshold_high && state.RemainingSeats >= seat_threshold_low)
                {
                        if (state.RemainingDays > remainingday_threshold)
                        {
                                return 1;//sell
                        }

                }
        }
        return 0;//no sales
}