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The newsletter of the SIE de Investigación y Enseñanza N. 33 - November/December 2009

Screen: the best thing since sliced bread for workers@home

If you always work in the same computer, screen probably will not offer you much. But if you routinely have to work from different places, screen can be your next best friend. Screen is a terminal multiplexer that allows you to manage many processes through one physical terminal and offers the ability to detach from a session and then attach to it at a later time. When detached from a session, the processes screen is managing continue to run. You can then re-attach to the session at a later time, and your terminals are still there, the way you left them. You can learn a bit more about screen with the following tutorial, which introduces the following scenario to lure you:
"You are logged into your remote server via SSH and happily plucking along at your keyboard and then it happens. Suddenly, the characters stop moving and then you get the dreaded "Connection Closed" message. You have just lost your session. You were halfway through some task and now you have to start over. Ugh. Well you can prevent this from happening by using screen. The Linux screen tool can not only save you from disconnection disasters, but it also can increase your productivity by using multiple windows within one SSH session."

IDL jobs in Condor

A recurring question to us has been whether IDL jobs can be run with Condor. So far, our use of IDL with Condor was limited by the number of available licenses at any given time (which meant that perhaps you could run 50-60 jobs simultaneously), until we discovered the IDL Virtual Machine which lets you run an IDL "executable" file without the need for licenses (most of you probably know the necessary steps to create a SAVE file, but if in doubt see here for an example on how to create such a file).

The problem is that the IDL Virtual Machine is meant to be run interactively in a server with X running and Condor is not particularly well suited for this. But you can manage it with a little ingenuity. We have written a little program to take care of all the details and overall it works without any problems: now we can submit hundreds of IDL jobs simultaneously to our Condor pool! If you are interested (or think you will be in the future), please let us know, and we'll set you up (or read the details by yourself at the SIEpedia).

Welcome to the IAC Computing Services!

One of the topics discussed in the last meeting of the SIE+SIC Users Committee was the information that new users that have just joined the Institute receive about the IAC Computing Services. The general opinion was that they get next to none, and they struggle to find their way around by discovering things themselves or by asking coworkers and office mates. We thus decided to create a "welcome mail" that provides a short introduction to the IAC computing services, answers some basic questions and doubts newcomers usually have, and points to several web pages where they can find extensive and detailed documentation on many topics. This email message is automatically put into the user's mailbox when their account is created. Even if you have worked at the IAC for more years than you care to count, still you may find the Welcome to the IAC Computing Services useful: give it a read!

Strange Mathematica quirk

Some users have reported that Mathematica behaves oddly with 3D graphics. Instead of displaying the gorgeous 3D plot you expect, it shows an empty box, which however you can manipulate with the cursor, with the 3D plot sometimes making a momentary appearance. Strangely enough, this quirk only shows up in some machines, while in others 3D graphics works just fine. While we were unable to find any clear explanations, nevertheless we found a workaround, which consists in starting mathematica with the command:
( setenv LD_LIBRARY_PATH "" ; mathematica ).
This problem and its solution have been immortalized in our SIE forum, see http://venus/SIE/forum/viewtopic.php?f=7&t=212. In two other posts, you can find what to do when you are ssh-ing to another machine and you get the greatly alarming message WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!, and how to avoid a longish wait after telnet-ing to

Not all programming languages are born equal

In a past newsletter we mentioned the "99 bottles of beer" page, where hundreds of different programming languages are used to write a simple program. Although most of these languages never make it into the "real" world, there is still plenty of choice amongst the mature ones. Perhaps the most visible difference is the syntax (which the 99 bottles of beer page highlights, although more interesting is the Rosetta Code page), but more important differences are based on the paradigms and type systems used (you can see a comparison in Comparison of programming languages) and their performance (see for instance The Computer Language Benchmarks Game to see how your favourite language scores). Also important (for resources and the support that you can get from other programmers) is the popularity of different programming languages (see for instance Programming Language Popularity).

Second Practical Course of the Spanish Virtual Observatory

Though you have probably already read the mail about it, we would like to remind you about the "Second Practical Course of the Spanish Virtual Observatory", a workshop on using Virtual Observatory tools, that will take place here at the IAC on 4-5 March 2010. Full details can be found at the Segundo Curso Práctico de la Red Temática SVO. La Laguna, 4-5 marzo 2010 page. The deadline for registration is Friday 19 February 2010.
SIE de Investigación y Enseñanza :: N. 33 - November/December 2009 - Contact: