I want to announce that I successfully finished my thesis research with an 8. Feel free to read the final version of my report. Thanks for reading!
Colin Schepers  Automatic Decomposition of Continuous Action and State Spaces in SimulationBased Planning (2012)
Some aditional work (most never intended for distribution):
Colin Schepers  Searching in networks (2010 / Maastricht University / Bachelor Thesis)
Artificial Intelligence for Ming Mang (2011 / Maastricht University)
NAO Robots lifting a table (2011 / Maastricht University)
Blokus3D Solver (2012 / Purpose: Learning C# / WPF)
Colin Schepers' Blog
Master Thesis Artificial Intelligence
Wednesday, July 25, 2012
Monday, June 4, 2012
Feedback 04062012
Results
Donut World
 Step limit: 10 steps per episode
 Reward: +1 for being on the donut, 0 otherwise
 Gaussian noise added to the rewards: mean = 0, sigma = 0.5
 Optimal reward equals 7 because of turning the first 3 steps
 Results averaged over 10,000 episodes
 Algorithm MC randomly samples 10step trajectories and plays the best found
 LTT is the "Levelbased Transposition Tree" with first a regression tree discretizing the state space and each leaf of this tree holds a regression tree discretizing the action space (for that region of the state space).
 MTT is the "Mixed Transposition Tree" which is only one regression tree but also splits on the state space.
 Random performs worst, followed by MC.
 Performance wise, STL > RTL and then HOO > IRTI
 LTT performs about average in comparison with the four algorithms mentioned above. MTT performs bad in comparison with the other algorithms (probably due to the problem stated in the previous post), but is still better than MC and Random.
 Obviously MC and Random are the fastest algorithms
 HOO is the slowest and the plot shows its running time of O(n^2)
 TT is a bit slower than RMTL and RSTL, probably due to that fact that they reuse the same tree build in previous realworld steps.
 Initially MTL is a bit faster than STL, but MTL's computational complexity is slightly higher (due to the perfect recall).
Thursday, May 31, 2012
Feedback 31052012
Work
 Presentation last Tuesday went fine. Kurt gave me one tip regarding the Transposition Table; I could mix the state and action space in stead of the level based approach. At a second though this should indeed be better, because splits then can only occur at leafs which means recalling is only done from the leaf to one of the two children (in stead of possibly "rebuilding" a whole new tree structure).
 The socalled Mixed TT is very similar to a regular Regression Tree. In stead of only splitting the action space it can also split the state space. During the selection step the agent chooses the best UCT child in case the node splits the action space and when at a node which splits on the state space the child is chosen according to the current state in the simulation. Each single action updates the tree in stead of a sequence of actions in case of TLS. The tree that is build can again be reused for later steps.
 I ran an experiment again for the new transposition tree and it comes very close to the best technique RMTL.
 When trying the Mixed TT in combination with HOO (i.e. HOO with state information) I found out this problem: since HOO splits on random dimensions it sometimes occurs that the very first split is on the action space. This means that no matter in which state the agent is in, is will always pick the region of the action space with the best UCT value (which could lead to bad actions if previously the other child was better)? This makes me wonder if the idea behind the Mixed TT is correct and why for regression trees is works so well (probably due to the intelligent splitting which initially splits on the state dimension representing the angle of the pole)?
 Furthermore, not very unimportant (!) I found an small error applicable to the HOO based algorithms. After fixing this and some parameter tuning (raising n_min), I achieved some better results. HOMTL is now reaches 50% succes rate but HOSTL is still computationally too expensive to plan ahead enough steps (the biggest problem is when the cart reaches the left or right "wall", then agent then has to force the pole's angle respectively to the right or left to get away from this wall).
Succes
rate

Average
payoff


RMTL

94%

971.747

RSTL

85%

922.047

HOMTL

50%

706.525

HOSTL

5%

320.255

Levelbased TT

65%

808.480

Mixed TT

87%

924.698

MC

9%

389.590

Sunday, May 27, 2012
Feedback 27052012
Work
 Looked into the perfect recall and fixed it. RMTL is able to balance for 1000 steps 94% (vs 69% before). I've updated the table from a couple of posts back and for also provided it below in this post.
 Implemented the transposition tree and works pretty well. For the CartPole environment it performs better than Random, MC, HOMTL and HOSTL (see table). Offline it does not very good and probably lacks information about important states (not provided in the table).
 I removed the number of simulations from the table as in my opinion they were not really comparable anymore since I changed the parameters for HOO so it could achieve more simulations (but less information). Furthermore, the Transposition Tree Agent actually updates the tree structure each step (and not each simulation). Meaning that after 1 rollout, it can actually update 20 times (depending on the length of the rollout). Therefore I chose to remove them out of the table.
 I rerun the noisy Donut World experiment but now with reward noise. I appeared that there is no significant decrease in performance caused by this noise. Furthermore, I tried the transposition tree agent for this environment and it performed better than all other algorithms.
Succes
rate

Average
payoff


IRTI + TLS

94%

971.747

IRTI + HOLOP

85%

922.047

HOO + TLS

0%

77.254

HOO + HOLOP

3%

273.525

Transposition Tree

65%

808.480

MC

9%

389.590

Friday, May 25, 2012
Meeting 25052012
Action Points
 We started with discussing the planning proposed at the beginning of the year. For me, I was pretty accurate, except that I did not yet implement the "transposition tree" and the writing which started a bit later.
 We should use noise for the reward in stead of on the actions because if adding noise to the action can also change the optimal reward function, i.e. even when playing the best actions one would not be able to achieve the best reward. To draw the optimal line when having noisy actions you'd have to calculate products / intervals (to keep it general).
 For multi step results I should also make a MTLUCT agent
 I asked what to do with the state information of my "transposition tree". Michael proposed an idea and I brainstormed with Andreas afterwards:
 Assume the state/observation space to be Markov
 First level is an "observation tree", discretizing to observation space.
 Each leaf representing a region of this space links to an action tree on the second level, discretizing the action space and keeping information about which actions are best for the observation range from the level above.
 This observationaction tree can be reused for each state the agent is in due the the property of 1.
 Change last experiment so that noise is on rewards.
 Add the MTLUCT agent to the experiment
 Look into the global/perfect recall again
 Implement the "transposition tree"
 Writing
Friday, May 18, 2012
Feedback 18052012
Results
I've run the CartPole experiment again with more challenging properties:
[1] H. Van Hasselt and M. A. Wiering, “Reinforcement learning in continuous action spaces,” in Approximate Dynamic Programming and Reinforcement Learning 2007 ADPRL 2007 IEEE International Symposium on, no. Adprl, pp. 272–279, 2007.
Sinus environment: timebased
Six Hump Camel Back environment: timebased
CartPole environment: timebased
I've run the CartPole experiment again with more challenging properties:
 Goal: balance the pole for 1000 steps
 Payoff:
 For each step that the pole is balanced: +1
 If the pole's angle is > 12 degrees from upright position: 1 (and terminal state)
 Maximum expected payoff of 1000 due to the goal's statement
 Added Gaussian noise with standard deviation of 0.3 to both rewards and actions
 See [1] for more detailed description of the environment properties
 Agent's evaluation time per step: 50 ms
Succes
rate

Average
payoff


IRTI + TLS

94%

971.747

IRTI + HOLOP

85%

922.047

HOO + TLS

0%

77.254

HOO + HOLOP

3%

273.525

Transposition Tree

65%

808.480

MC

9%

389.590

[1] H. Van Hasselt and M. A. Wiering, “Reinforcement learning in continuous action spaces,” in Approximate Dynamic Programming and Reinforcement Learning 2007 ADPRL 2007 IEEE International Symposium on, no. Adprl, pp. 272–279, 2007.
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