Extreme Gammon

 Rollout settings

 From: pontiac Address: hmkg54@hotmail.com Date: 13 January 2012 Subject: problem Forum: BGonline.org Forums

```Hi extremegammon.  Can you explain briefly what is variance reduction and
truncate mean?  Why we use or should not use them?
```

 eXtreme Gammon  writes: ```Variance reduction ------------------ Variance reduction is a process that will adjust the result of each game played during a rollout by the luck of each roll. On the long run this is a 0 effect on the final equity but it allows rollouts to converge much faster. This reduces greatly the amount of trials you need to get to get an accurate result. For instance in your position rolling out 23/13 with VR (3-ply 2592 games) with Variance reduction your confidence interval is 0.012 (meaning that there 95% confidence that a rollout with infinite number of trial will be within 0.012 equity of the result reported). Without variance reduction the confidence interval is 0.087 and it will take 136,242 trial to get the same confidence (Confidence interval decrease as the square root of the number of game: i.e. rolling 4 time more game will decrease the confidence by a factor 2). This setting should always be on. I am considering to remove it as an option for rollout. Truncation ---------- Truncation means that after N dice roll the rollout will stop and the position evaluated using the truncation level. This result in much less variance, but it can create problem if the positions after this N move is not evaluated very accurately. I do not advice to use short (anything less than 7) truncation. Roll for both No double and Double ---------------------------------- Applies only to checker play and if the opponent can double. If this option is checked the program will roll the position twice one if the opponent doesn't double, once if the opponent doubles. It will report the best decision. This can be an useful settings if you suspect the computer will get the very next cube decision wrong. It has a cost in term of speed: rollout using this setting are about 25% slower. Level ----- The stronger the level the more trustworthy a rollout is. But this come as a cost: TIME. Increasing from N-ply to (N+1)-ply will make the rollout about 20 times slower. Ultimately it depends on how much time you want to spend, what computer you have etc Conclusion ---------- Rollout settings are a difficult subject: explaining what is the best setting is extremely complex as it depends largely on what the user is looking for, what time they are willing to spend and what hardware they have. ```

### Extreme Gammon

Extra elements in a MAT file  (eXtreme Gammon, Dec 2009)
Rollout settings  (pontiac+, Jan 2012)