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Model
A model is an agent's representation of the environment. It is similar to the mental models we have about people and things around us. An agent uses its model of the environment to predict what will happen next. There are two key pieces to it:
: The state transition model/probability
: The reward model
The state transition model 
is a probability distribution or a function that predicts the probability of ending up in a state 
in the next time step 
given the state 
and the action 
at time step 
. Mathematically, it is expressed as follows:
The agent uses the reward model 
to predict the immediate next reward that it would get if it were to take action 
while in state 
at time step 
. This expectation of the reward at the next time step 
can be mathematically expressed as follows:
