S5R2

Hi!

We're near the end of the intermediate S5RI run and thus about to start the long-awaited S5R2. Some properties of S5R2 still change faster than I can type and would be hopelessly outdated when you read them, but I'd like to give you some impression of what's more or less fixed now.

The "science run #5" of the LIGO instruments, or S5 for short, gives us not only the most sensitive data, but also the largest amount of data we ever had. This is very good in terms of science, as the sensitivity of the search for continuous signals increases with "observation time", i.e. the length of the data available.

However, with our present analysis tool, the computation time needed grows to the power of six over the amount of data. It's obvious that we need something more clever to deal with a larger amount of data, so we developed a new program which we call "Hierarchical Search". The basic idea is to first scan the parameter space with a coarse "grid" and then only take a closer look at the areas that have been detected as interesting, in a "follow-up stage". The current code is designed to do only the first stage, it had not been decided yet if we will do a follow-up stage on Einstein@Home as well or e.g. on LSC clusters.

The application we'll use for this run is all new and has never been used before. The algorithm used in the old App is still a part of the new one, and other parts have also been used before, but they have never been used in the present combination, and in particular not in a distributed computing project of that scale. We expect some problems to arise from this.

One of the issues we are still working on is some "overhead", i.e. calculations that are performed for technical reasons, but don't actually contribute to the result, thus wasting computing power.

We therefore will set up S5R2 as a short, experimental run that limits the search to parts of the parameter space where the overhead is well under control. During this short run we will improve the Application in various aspects. The results will also help us tuning the parameters for the next, larger run (probably named S5R3).

With the amount of data to be analyzed, however, also grows the amount of data to be downloaded to your machines. To save bandwidth both on your and on our side, we developed a new scheme for data files. They are split into small files of about 3MB in size (that are somewhat re-combined in the App). When there is no more work available for the data files you already have on your machine, the scheduler will try to assign work to your host that minimizes the number of files you have to download, so you should in most cases get away with a new download of only two files (~6MB).

However, a complete set of files (that will be used for many tasks you get) can consist of up to 10 files, so the initial download can be more than 40MB (including the Application and other data files that need to be downloaded only once per run). This might be not suitable for dial-up / modem users anymore.

We are running out of S5RI work, and thus as usual your clients will have to download a new data file for only a few workunits anyway, so modem users: beware.

We expect to issue the first hundrets of S5R2 Workunits some time tomorrow.

At the beginning Apps will be available only for our major platforms (Windows-x86, Linux-x86, MacOS-PPC and MacOS-x86); other platforms will follow with time. I hope to get the Apps finished before the last results of S5RI are sent out.

BM