2011.03.25 in Milkyway

Milkyway N-body 0.40

I've just finished making the next release of the Milkyway@Home N-body simulation. These should start going out soon along with new searches. The major change in this version is that Lua is now used for configuration instead of the old static JSON file. You can now script a totally arbitrary initial particle distribution, and you can run a simulation without the milkyway background potential, so it's probably more useful for anyone else to use now for other N-body simulations.

This all started one night when I was planning on finishing the few remaining issues with the new CAL/CAL++/ATI Separation application, but needed to get some reference results from the working OpenCL application on Nvidia. But then Tim Horton left Jayne (the system with the GTX 480 donated by a Milkyway@Home user) running Windows and disappeared somewhere. Then there was something of an obstacle to doing what I was planning on doing and I thought it would be cool to have an embedded dynamic language. My original thought was to use JavaScript after Seed, but JavaScriptCore isn't really split out from Webkit, and the full Webkit dependency was too much for what I needed. I considered Python, but the Lua libraries were an order of magnitude smaller, so I chose it and spent the next few days getting basic things working. I spent a long time writing boring bindings for many of the structs for the N-body simulation. I later found that if I had used LuaJIT, it seems it would have done most of the work for me. About a week later I had something working. Although the mini-API isn't really close to what I originally envisioned or wanted, you can now script any simulation you want. I'm considering making it possible to use a Lua closure for the external potential, but I'm not sure how much slower that will be.

This enables more complex models to be fit without a need to make new releases, and avoids a need to mangle the code every time the model changes to support more combinations of features. The current plan is to try multi-component dwarfs, with an extra component of dark matter which will be ignored in the final likelihood calculation.

I've fixed a few other small random bugs, such as in some cases on Windows some system IO error would happen when checkpointing, and there would be a "something something failed: No error" type error message. I'm also using newer BOINC libraries for Linux to hopefully avoid the random crashes which were coming from the 6.10.58 libraries.

I've switched to only using the multithreaded versions using OpenMP for all systems. The 64-bit Windows build is now actually 64 bit as well. Building on Windows is still an agonizing process (mostly getting dependencies and a functioning build environment, not actually building it) I don't understand, but it's getting better.

You can download the source here.

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