In this weekly workshop we will discuss how to set up N-body simulations in virtual worlds, starting with Second Life, and moving on to OpenSim and other worlds. We are planning to start a wiki on which we provide a complete open-source description of our algorithms and their implementations, together with elementary introductions to the mathematics and physics of Newtonian gravity, and numerical methods used to solve the differential equations that correspond to Newton's laws.
The basic idea is to start a kind of N-body wikipedia, as a group's process. It should be self contained, a place to gather all the basic information that is currently missing from the literature. Up till now, if you want to write a decent N-body code from scratch, you have to somehow catch the oral knowledge that is floating around in the community, most of which has never been written down. We want to change that.
One place to start is the open-source introductory text written over the last several years by Piet Hut and Jun Makino, "Moving Stars Around"; see http://www.artcompsci.org/#msa where we give pointers to two versions. The older one is written using C++ and the newer one, with even more detailed background, uses Ruby. We propose to use the basic text, and to translate the (rather short) pieces of code into other languages, starting with LSL, the Linden Scripting Language, and then to move on to OpenSim.
There are many ways we can grow a kind of N-body Wikipedia, and starting with "Moving Stars Around" was just one early suggestion. We have created a stellar dynamics wiki where we have started to experiment with various approaches.
2009.09.24 : 7am SLT : Report on a Workshop on Star Cluster Evolution in Tokyo
Speaker: Piet Hut, Institute for Advanced Study, Princeton, NJ, USA.
A brief report will be given of an ongoing workshop on Star Cluster Evolution in Tokyo, Japan. The workshop will be held in two locations: NAOJ, the national astronomical observatory in Japan, and NII, the national institute for informatics. Please contact Piet Hut at
for additional information about the schedule. After the report, we will engage in a general discussion between those who were present at the RL meeting in Tokyo and those who will be present only virtually in SL.
Speaker: Jun Makino, National Astronomical Observatory Japan, Tokyo.
An update will be given of the current status of the GRAPE-DR project. The GRAPE-DR chip is the next-generation hardware for N-body simulation. Unlike the previous GRAPE hardware, it is a programmable SIMD machine with a large number of simple processors integrated into a single chip.
The GRAPE-DR chip consists of 512 simple processors and operates at a clock speed of 500 MHz, delivering a theoretical peak speed of 512/256 Gflops (single/double precision). A 128-node cluster, each node with a 4-chip GRAPE-DR card is now in operation. We plan to extend this system to 256-512 nodes with two or three cards per node, to achieve a speed in the range of 1 Pflops.
2009.07.09 : 7am SLT : "From MUSE to AMUSE: a toolbox for more than stellar dynamics"
Speakers: Arjen van Elteren and Inti Pelupessy, astrophysics grad students at the University of Leiden, Holland.
Simulating astrophysical objects requires a combination of different physics operating on different length and time scales. For example, in a star cluster that is in the process of being born, stars move around under the influence of gravity while sending out radiation and heating the interstellar medium gas from which they were born. In our presentation, we will introduce the MUSE and upcoming AMUSE packages for astrophysics. These packages aim to simplify the integration of multiple codes that each simulate some aspect of the physics involved so that complicated simulations are easier to run.
2009.07.02 : 7am SLT : "More on Grav-Sim: Gravitational Simulation on a Desktop Computer"
Speaker: Mark Ridler (SL: Ridlero Rioccan), project manager and C++ developer
Following his earlier Mica Simulations talk on 11th June, Mark Ridler will host a Grav-Sim Q & A session. He will present a brief progress report, including:
Grav-Sim uses an evolution of the "Art of Computational Science" code provided by Piet Hut and Jun Makino on www.artcompsci.org. Mark has ported it to C++ in his spare time and now has a version with many additional features that he is presenting to Mica Simulations.
Please take the time to read the text for the 11th June presentation in the article:
You may like to download version 1.01 (which has also been compiled on unix by Peter Teuben).
2009.06.04 : 7am SLT : "ASTROSIM: how to get it working as a permanent exhibition in MICA"
Moderators: Piet Hut (SL: Pema Pera), prof. of astrophysics and interdisciplinary studies at IAS, Princeton, and Arturo Nakasone (SL: Jeremiah Renfold), postdoctoral fellow at NII, the National Institute for Informatics, Tokyo, Japan.
Two weeks earlier, Arturo blew us all away with his demo of AstroSim, showing us smooth motions of up to a thousand stars in SL, something most of us had thought to be completely unobtainable. The trick that Arthur used was to bypass the Linden Scripting Language, and instead use a bot, a robot avatar, through which he piped his instructions at great speed directly from his own computer. This time, we will have a discussion concerning the possibility of installing AstroSim as a permanent exhibition in MICA.