Modeling limit order trading with a continuous action policy for deep reinforcement learning.

Limit Orders allow buyers and sellers to set a "limit price" they are willing to accept in a trade. On the other hand, market orders allow for immediate execution at any price. Thus, market orders are susceptible to slippage, which is the additional cost incurred due to the unfavorable execution of a trade order. As a result, limit orders are often preferred, since they protect traders from excessive slippage costs due to larger than expected price fluctuations. Despite the price guarantees of limit orders, they are more complex compared to market orders. Orders with overly optimistic limit prices might never be executed, which increases the risk of employing limit orders in Machine Learning (ML)-based trading systems. Indeed, the current ML literature for trading almost exclusively relies on market orders. To overcome this limitation, a Deep Reinforcement Learning (DRL) approach is proposed to model trading agents that use limit orders. The proposed method (a) uses a framework that employs a continuous probability distribution to model limit prices, while (b) provides the ability to place market orders when the risk of no execution is more significant than the cost of slippage. Extensive experiments are conducted with multiple currency pairs, using hourly price intervals, validating the effectiveness of the proposed method and paving the way for introducing limit order modeling in DRL-based trading.