Wednesday, June 11, 2008

About xmonad in Russian

Finally, the first part of our (with Ivan Veselov) xmonad article is published! You can download it from after free registration.

The goal of the article is to promote xmonad and gain new users. So the intended audience is people who never heard about xmonad and haskell or xmonad newbies. Article explains the main steps in configuring xmonad.

The next two parts of the article will be published in the following issues of the journal. At the end I'll publish html version somewhere, probably in xmonad wiki.

Thanks to the people who reviewed our work and provided useful comments:

  • Dmitry Astapov
  • Oleg Tsibulsky
  • Dmitrij Czarkoff
  • Konstantin Barabanov
  • Dmitry Shurupov
  • Alexander Solovyov
  • Marina Sulim

Friday, June 6, 2008

Revisiting real analysis

Real analysis is famous for its counterexamples. It's usually not obvious how to find these examples, and that irritated me, because I needed to learn them by rote. Well, today I reduced number of unobvious counterexamples by one.

Today I examined one girl from 10th grade in calculus, and she got Darboux theorem. After she proved the theorem, I asked, is it a consequence of Bolzano's theorem. "No, because derivative may not be continuous". "Can you then show me an example of differentiable function, whose derivative isn't continuous?"

She couldn't, so I had to ponder it myself. Of course, I didn't remember the example.

The first try was to integrate some non-continuous function, but it cannot succeed — we have no guarantee that integral will be differentiable.

Then I looked at Darboux theorem again. Intermediate value property is very strong — ordinary discontinuous functions don't satisfy it and therefore cannot claim to be a derivative. If derivative is monotonic in some neighbourhood of a point, then intermediate value property force it to be continuous in that point. Now it becomes clear that we want to search for a function, which oscillates infinitely frequently in the neighbourhood of a point. So, sin(1/x) naturally comes to mind. It remains to multiply by x2 to achieve necessary degree of smoothness, and here it is!

Thursday, June 5, 2008

Walter Gander's talk

CAS topic becomes hot! Odessa polytechnic university invited Prof. Walter Gander to give a talk about using Maple and MatLab.

I understand how hard it is to prepare a talk when you have no clue about your auditory, but finally the lecture was quite poor.

Prof. Gander just showed several problems and their solutions obtained using mentioned software, but honestly it wasn't very exciting.

Another issue was completely non-technical translator. I'm not sure if anybody really needed a translator at all, but that one was a real disaster.

On the other hand, this is second time during the month when politechnic university invites somebody to give a talk (see Sun university day). Good trend!

Sunday, June 1, 2008

Impressions from Mathematica Tour

As I said, I've attended Oleksandr Pavlyk's presentation of Mathematica 6 features, which was held on May 30 at Kiev-Mohyla university.

Lecture went off very well. Also there were many jokes both from the lecturer and from the auditory. There were about 15 people, roughly equally students and adults.

Oleksandr answered many of my questions. Here's what I found out:

  1. 2/3 of Mathematica kernel is written in C and 1/3 in Mathematica itself; also they use some libraries written in other languages.
  2. I wrote about my frustration with the new help system. Oleksandr responded that this was done to make help an ordinary Mathematica notebook, and the old system was a "dirty hack". Another reason is huge growth of the documentation volume.
    WR is aware of slowness of help system on Linux — they think it's related to Java performance on Linux, and Java is somehow involved in displaying documentation.
  3. Mathematica uses number of opensource libraries (LAPACK was mentioned). They contribute back in form of bug reports.
  4. Their researchers publish papers, but they don't maintain anything like papers page by Google, as they don't see need for it. Oleksandr suggested searching the papers through Google scholar.
  5. There are free on-line seminars on, and they include not only training on some Mathematica topic, but also "talks with devs".

From the presentation I also learned about few new features in version 6, which looks quite useful.

  1. Manipulate makes experimenting with parameters easy. Although it looks like one of those bells&whistles in Mathematica 6, I find it useful.
  2. RegionPlot is definitely a great thing, which I missed many times.

At the end there was training session, where everybody had an ability to try new features under the supervision of Oleksandr. There I got acquainted with Vladimir Bondarenko from Simferopol, who does very effective testing of computer algebra systems.