It was twenty years ago today . . .

16/08/2011

With these beautiful words starts a recollection paper by the founder of arXiv, Paul Ginsparg. This is worth the reading as this history spans a number of years exactly overlapping the computer revolution that definitely changed our lives. What Paul also changed through these new information tools was the way researchers should approach scientific communication. It is a revolution that is not stopped yet and all the journals I submit my papers have a link to arXiv for direct uploading of the preprint. This change has had also a great impact on the way these same journals should present to authors, readers and referees as well at their website.

For my readers I would like just to point out how relevant was all this for our community with the Grisha Perelman’s case. I think all of you are well aware that Perelman never published his papers on a journal: You can find both of them on arXiv. Those preprints paid as much as a Fields medal and a Millenium prize. Not bad I should say for a couple of unpublished papers. Indeed, it is common matter to have a paper largely discussed well before its publication and often a preprint becomes a case in the community without not even seeing the light of a publication. It is quite common for us doing research to console colleagues complaining about the harsh peer-review procedure by saying that today exists arXiv and that is enough to make your work widely known.

I was a submitter since 1994, almost at the very start, and I wish that the line of successes of this idea will never end.

Finally, to prove how useful is arXiv for our community, I would like to point out to you, for your summer readings a couple of papers. The first one is this from R. Aouane, V. Bornyakov, E.-M. Ilgenfritz, V. Mitrjushkin, M. Müller-Preussker, A. Sternbeck. My readers should know that these researchers always do a fine work and get important results on their lattice computations. The same happens here where they study the gluon and ghost propagators at finite temperature in the Landau gauge. Their conclusion about Gribov copies is really striking, comforting my general view on this matter (see here), that Gribov copies are not essential not even when one rises the temperature. Besides, they discuss the question of a proper order parameter to identify the phase transition that we know exists in this case.

The next paper is authored by Tereza Mendes, Axel Maas and Stefan Olejnik (see here). The idea in this work is to consider a gauge, the $\lambda$-gauge, with a free parameter interpolating between different gauges to see the smoothness of the transition and the way of change of the propagators. They reach a volume of 70^4 but Tereza told me that the errors are too large yet for a neat comparison with smaller volumes. In any case, this is a route to be pursued and I am curious about the way the interpolated propagator behaves at the deep infrared with larger lattices.

Discussions on Higgs identification are well alive yet ( you can see here). take a look and enjoy!

Paul Ginsparg (2011). It was twenty years ago today … arXiv arXiv: 1108.2700v1

R. Aouane, V. Bornyakov, E. -M. Ilgenfritz, V. Mitrjushkin, M. Müller-Preussker, & A. Sternbeck (2011). Landau gauge gluon and ghost propagators at finite temperature from
quenched lattice QCD arXiv arXiv: 1108.1735v1

Axel Maas, Tereza Mendes, & Stefan Olejnik (2011). Yang-Mills Theory in lambda-Gauges arXiv arXiv: 1108.2621v1

CUDA: Lattice QCD on a Personal Computer

21/01/2011

At the conference “The many faces of QCD” (see here, here and here) I have had the opportunity to talk with people doing lattice computations at large computer facilities. They said to me that this kind of activities imply the use of large computers, user queues (as these resources are generally shared) and months of computations before to see the results. Today the situation is changing for the better due to an important technological shift. Indeed, it is well-known that graphics cards are built with graphical processing units (GPU) made by several computational cores that work in parallel. Such cores do very simple computational tasks but, due to the parallel architecture, very complex operations can be reduced to a set of such small tasks that the parallel architecture executes in an exceptionally short time. This is the reason why, on a PC equipped with such an architecture, very complex video outputs can be obtained with exceptionally good performances.

People at Nvidia have had the idea to use these cores to do just floating point operations and use them for scientific computations. This is the way CUDA (Compute Unified Device Architecture) was born. So, the first Tesla cards without graphics output, but with GPUs, were produced and the development toolkit was made freely available. Nvidia made parallel computation available to the masses. Just mounting a graphics card with CUDA architecture it is possible for everybody to have a desktop computer with Teraflops performances!

As soon as I become aware of the existence of CUDA I decide to mount on this bandwagon opening to me the opportunity to do QCD on the lattice at my home. So, I upgraded my PC at home with a couple of 9800 GX2 cards (2 GPUs for each with 512 MB of DDR3 RAM each one) having CUDA architecture 1.1. This means that these cards can do single precision computations at about 1 Tflops and my PC can express a performance of 2 Tflops. But I have no double precision. I have also changed my motherboard to a Nvidia 790i Ultra that support a 3-way SLI mode and the power supply upgraded to 1 KW (Silent Gold Cooler Master). I have added 4 GB of DDR3 RAM and maintained my CPU, an Intel Core 2 Duo E8500 with 3.16 GHz for each core. The interesting point about this configuration is that I have bought the three Nvidia cards from Ebay as used material at a very low cost. Then, I was in business with very few bucks!

Before this upgrading of my machine I had Windows XP home 32 bit installed. This operating system was only able to address 3 GB of RAM and 1 GB of it was used by the two graphics cards. This revealed a serious drawback to all the matter. In a moment I will explain what I did to overcome it.