:orphan: discount ******** .. note:: Discount factors are only implemented in the learning mechanisms *Guided associative learning*, *Expected SARSA*, *Q-learning*, and *Actor-critic*. Specifies the discount factor, written as :math:`\gamma` in :ref:`the equations for memory updates`, that tells how important future rewards are to the current state. The discount factor is a value between 0 and 1. A reinforcement value :math:`u` that occurs :math:`N` steps in the future from the current state, is multiplied by :math:`\gamma^N` to describe its importance to the current state. For example, consider :math:`\gamma=0.9` and a reinforcement value :math:`u=10` that is 3 steps ahead of the current state. The importance of this reward to the subject from where it stands is equal to :math:`10 \cdot 0.9^3 = 7.29`. The value of the parameter ``discount`` is used in the updating equations described in :ref:`the mechanisms`. Syntax ------ :: discount = v where ``v`` is a :ref:`scalar expression`. Description ----------- ``discount = v`` sets the discount factor to ``v``. Examples -------- :: discount = 0.5 sets the discount factor to 0.5. :: @variables x = 0.5 discount = x + 0.1 sets the discount factor to 0.6.