This is the supposedly-bimonthly-but-we-keep-skipping 'What are you working On?' thread. Previous threads are here. So here's the question:

What are you working on? 

Here are some guidelines:

• Focus on projects that you have recently made progress on, not projects that you're thinking about doing but haven't started.
• Why this project and not others? Mention reasons why you're doing the project and/or why others should contribute to your project (if applicable).
• Talk about your goals for the project.
• Any kind of project is fair game: personal improvement, research project, art project, whatever.
• Link to your work if it's linkable.

If it's worth saying, but not worth its own post, even in Discussion, it goes here.

http://blog.regehr.org/archives/546

John Regehr, an associate professor of computer science at the University of Utah, writes about two algorithmic optimizations for Conway's Game of Life, and speculates on the implications for self-aware entities in simulations.

Hashlife is a clever optimization that treats the Life grid as a hierarchy of quadtrees. By observing that the maximum speed of signal propagation in a Life configuration is one cell per step, it becomes possible to evolve squares of the Life grid multiple steps into the future using hash codes. Hashlife is amazing to watch: it starts out slow but as the hashtable fills up, it suddenly “explodes” into exponential progress. I recommend Golly. Hashlife is one of my ten all-time favorite algorithms.

Those who have read Greg Egan's Permutation City will find the concept of Hashlife familiar.

Another ingenious simulation speedup (developed, as it happens, around the same time as Hashlife) is Time Warp, which relaxes the synchronization requirements, permitting a processor to run well ahead of its neighbors. This opens up the possibility that a processor will at some point receive a message that violates causality: it needs to be executed in the past. Clearly this is a problem. The solution is to roll back the simulation state to the time of the message and resume execution from there. If rollbacks are infrequent, overall performance may increase due to improved asynchrony. This is a form of “optimistic concurrency” and it can be shown to preserve the meaning of a simulation in the sense that the Time Warp implementation must always return the same final answer as the non-optimistic implementation.