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The math that serves as the foundation for reinforcement learning is a Markov Decision Process (MDP). I am interested in representing pitching behavior by a MDP. I believe Value Iteration can help batters strategically counter a pitcher's pitch sequence. In order to compute the Value Iteration algorithm, I need a probability transition matrix.
pitcher_mdp.py is a Python script that creates a MDP class. This class is equipped with various methods for MDP related matter to conduct reinforcement learning. The method get_markov_chain() will generate a transition probability matrix (markov chain) among 12 pitch states,
(0,0)
(1,0)
(2,0)
(3,0)
(0,1)
(0,2)
(1,1)
(1,2)
(2,1)
(2,2)
(3,1)
(3,2)
Once you've generated a markov chain of the pitching states, you can pass it into the value_iteration() function. Value iteration will find the best sequence of actions (swing or stand) to maximize the expectation at each state.
Since pitcher_mdp.py is a Python class, we can instantiate it in another python file. For example, find_batting_strategy.py instantiates a pitcher_mpd object and generates a markov chain and calls the value iteration method.
If you want to visualize the markov chain (without actions) call the plot_markov_chain() function.
pitcher_mdp.py should take in most MLB pitchers. I use the pybaseball package to acquire pitching data for an individual player. In order to correctly get data from pybaseball follow the parser arguments in the find_batting_strategy.py file.
For example,
python find_batting_strategy.py \
--first_name Zac \
--last_name Gallen \
--start_dt 2022-04-16 \
--end_dt 2022-10-04