  In deep reinforcement learning, estimating the value function to evaluate the
quality of states and actions is essential. The value function is often trained
using the least squares method, which implicitly assumes a Gaussian error
distribution. However, a recent study suggested that the error distribution for
training the value function is often skewed because of the properties of the
Bellman operator, and violates the implicit assumption of normal error
distribution in the least squares method. To address this, we proposed a method
called Symmetric Q-learning, in which the synthetic noise generated from a
zero-mean distribution is added to the target values to generate a Gaussian
error distribution. We evaluated the proposed method on continuous control
benchmark tasks in MuJoCo. It improved the sample efficiency of a
state-of-the-art reinforcement learning method by reducing the skewness of the
error distribution.
