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arXiv 1302.5565cs.LG
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削波在神经控制中的重要性--基于成本函数的直接梯度下降法和自适应动态规划

The Importance of Clipping in Neurocontrol by Direct Gradient Descent on the Cost-to-Go Function and in Adaptive Dynamic Programming

City University London(伦敦城市大学)

Michael Fairbank

摘要:

在自适应动态规划、神经控制和强化学习中,智能体的目标是学习选择动作,以使总成本函数最小化。在本文中,我们表明,当离散时间被用来模拟代理的运动,它可以是非常重要的做“裁剪”的运动的代理在最后的时间步的轨迹。通过裁剪,我们的意思是轨迹的最后一个时间步将被截断,使得智能体精确地停止在到达的第一个终端状态,并且没有更远的距离。我们证明,当省略剪裁时,学习性能可能无法达到最佳;当剪裁正确时,学习性能可以显着提高。我们描述的裁剪问题影响使用环境的模型函数的显式导数来计算学习梯度的算法。这些包括反向传播通过时间控制,和基于双启发式动态规划的方法。然而,裁剪问题不会显著影响基于启发式动态规划、时间差异或策略梯度学习算法的方法。类似地,剪切问题不影响固定长度的有限时域问题。

英文摘要:

In adaptive dynamic programming, neurocontrol and reinforcement learning, the objective is for an agent to learn to choose actions so as to minimise a total cost function. In this paper we show that when discretized time is used to model the motion of the agent, it can be very important to do "clipping" on the motion of the agent in the final time step of the trajectory. By clipping we mean that the final time step of the trajectory is to be truncated such that the agent stops exactly at the first terminal state reached, and no distance further. We demonstrate that when clipping is omitted, learning performance can fail to reach the optimum; and when clipping is done properly, learning performance can improve significantly. The clipping problem we describe affects algorithms which use explicit derivatives of the model functions of the environment to calculate a learning gradient. These include Backpropagation Through Time for Control, and methods based on Dual Heuristic Dynamic Programming. However the clipping problem does not significantly affect methods based on Heuristic Dynamic Programming, Temporal Differences or Policy Gradient Learning algorithms. Similarly, the clipping problem does not affect fixed-length finite-horizon problems.

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