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HowTo build TaskWarrior from source without root privileges

born productivity, technology 2013-08-27

The new version of TaskWarrior (2.2.0) supports the new field scheduled which is/maybe pretty handy. The short version of how to install it on a linux machine (without asking root): Follow the instructions in the file INSTALL from the source tarball and set the flag DCMAKE_INSTALL_PREFIX of cmake to your home directory. Do you want to know more?

Kabel Deutschland HotSpots and WiFi MAC’s

rattle technology 2013-08-25

If you happen to be in Berlin, you can get 30 minutes of free WiFi in quite a lot of places from a KabelDeutschland™ HotSpot. Unfortunately, each connecting device gets only 30 minutes of free internet per day. On a completely unrelated note, I will talk about changing the MAC address of your WiFi card in Windows 7. I must, again, emphasize the fact that these two topics are in no way related. Do you want to know more?

Latex unter Windows mit Vorschau und deinem Lieblingseditor

born latex, technology 2013-07-12

Mein Eindruck ist, dass viele vernünftige Leute das Problem haben, unter Windows texen zu wollen und bei schrecklichen Programmen wie LaTeX Editor oder TeXnicCenter hängen bleiben. Prinzipiell funktionieren die ja auch. Vielleicht nicht perfekt und manchmal sind sie hier oder da etwas unpraktisch, oder stürzen ab (beim Editiern von Text) - aber sie tun ihre Arbeit und, hey, es gibt ja auch nichts besseres. Do you want to know more?

ssh / cygwin / windows quick & dirty

born technology 2013-07-01

This guide is for the people who only want to get this thing done where you only type

ssh remotehost

to ssh to your server at crazylongdomainname.com with the user u3321445longandunhandy on a windows pc with cygwin. Do you want to know more?

TaskWarrior: Tag Tasks as “maybe” and adjust the urgency accordingly

born productivity 2013-05-22

Today I stumbled across another useful feature of my beloved TaskWarrior: One can assign an urgency-coefficient to tags (and this coefficient can also be negative):

urgency.user.tag.maybe.coefficient=-100.0

I use the maybe-Tag to store ideas that I may or may not approach one day. Once a month and whenever I feel like doing something "useless", I can review the list and have every idea at one place (and I am always able to store such an idea). But of course I want to prevent +maybe tasks from showing up in reports like "next". This feature with a negative urgency-coefficient achieves exactly this. You can find more Options at the TaskWarrior documentation.

Building Perl stand-alone applications with a GUI using Mojolicious and PAR-Packer

tobi code, technology 2013-05-17

You might have come across the same problem I have faced pretty often: You want to write a small snippet of code for a friend who's not into programming to solve some task. You want to use the scripting language of your choice (yeah, [Perl](http://www.perl.org/)). But for many people, especially Windows users, explaining them how to [install perl](http://www.perl.org/get.html), install some modules from [CPAN](http://cpan.org), and finally how to use the script from the command line is tedious and often takes more time than writing it in the first place. And sometimes it even takes more time than solving the task by hand which is quite frustrating. So I always wanted to build stand-alone applications with a GUI for those cases. But building GUIs is usually a huge pain in the ass, so I always avoided it; until I got the idea to build web applications with [Mojolicious](http://mojolicio.us/) as GUI. Building stand alone executables without the need of installing perl, modules, or libraries can be solved with [PAR-Packer](http://search.cpan.org/dist/PAR-Packer/). So far, that was just a thought. A few days ago I got a small task: My brother wanted an application to automatically correct one kind of systemic error in large data sets. So I wanted to put that idea to the test. It worked out quite well! Do you want to know more?

The function field of a plane curve

rattle mathematics, remark 2013-05-13

My colleague and me were confronted with a question concerning the introductory chapter of a text on algebraic geometry. The scenario of a plane curve $C=Z(f)\subseteq \mathbb A_{\Bbbk}^2$ over a field $\Bbbk$ is considered, for a nonconstant polynomial $f\in\Bbbk[x,y]$. It was stated that the function field $\mathbb K:=\mathrm{Quot}(\Bbbk[x,y]/\langle f\rangle)$ is obviously of transcendence degree $1$ over $\Bbbk$ because $f(x,y)=0$ is a new relation between $x$ and $y$. The prerequisites to this text are basic undergraduate knowledge of algebra and topology. The question was about the obviousness of the above statement. We came up with a proof that only really requires some linear algebra. I found it rather cute. Do you want to see it?

My Quest for (CPU) Power

rattle code, technology 2013-05-11

This glab post is essentially about running a certain shell command remotely on multiple systems within a network that has been set up for public-key authentication. It's a standard task for experienced system administrators I am sure, but for me it was a little adventure in bash scripting — and I wanted to share it with you. Do you want to know more?

Getting rid of superfluous entries in the TrueCrypt chain loader

tobi technology 2013-05-08

I'm using TrueCrypt system encryption for my Windows Partition and use its chain loader to boot Linux via GRUB, which is installed on my /boot partition. However, at some point I also had GRUB installed on my root partition. Because of that the TrueCrypt boot loader — after pressing ESC when I didn't want to boot Windows — showed a list of partitions to boot from instead of directly starting the only other boot loader. That's less convenient and a little bit annoying, so I wanted to get rid of the entry. As the TrueCrypt boot loader seems to detect boot loaders on partitions automatically, I wanted to try deleting the redundant one. However, I didn't find anything on how to delete a boot loader from a partition; that's probably because it usually isn't necessary. A quick search on Wikipedia revealed that the boot loader on a partition is stored in the volume boot record (VBR) of the partition, which is just the first sector, similar to the MBR. So I first made a backup in case I got anything wrong ((make sure to backup to a different partition than the one you're going to write on :) )):

$ dd if=/dev/sda5 of=sda5.vbr bs=512 count=1

and then wrote zeros to the VBR:

$ dd if=/dev/zero of=/dev/sda5 bs=512 count=1

which did exactly what I wanted. Be aware, however, that when you want to delete the boot loader from an extended partition, this would overwrite the partition table in the extended boot record (EBR), so you may only overwrite the first 446 bytes of the sector instead of all 512. One last thing that cannot be stressed enough: Have a current and complete backup handy, and be prepared you might have to use it. I'm no expert on the subject. If the VBR is used for more purposes than just containing a boot loader as I expect, zeroing the whole sector may really go wrong.

Vector Bundles vs Locally Free Sheaves

rattle mathematics, remark 2013-04-30

I wrote a little text that outlines why vector bundles and locally free sheaves are the same thing. This approach is very messy with a lot of gluing, mostly because I did not look at Exercise II.5.18 in Hartshorne right away. The construction given there is much more canonical and preferable over mine. However, I decided to put this online simply because it is different and personally, it gave me a better feeling for why the two notions coincide.

Why Sudoku is boring

rattle code, remark, technology 2013-04-17

I was riding the backseat of a car, a pal of mine with a large Sudoku book on the seat beside me. I glared over at him and remarked that I find Sudokus utterly boring and would feel that my time is wasted on any of them. He looked up at me, clearly demanding an explanation for that statement. I continued to explain that a computer program could solve a Sudoku with such ease that there is no need for humans to do it. He replied that something similar could be said about chess, but still it's an interesting game. And it was then, that I realized why Sudoku is so horribly boring, and chess is not. It was the fact that I could code a Sudoku solver and solve the Sudoku he was puzzling about, and I would be able to do it faster than it would take him to solve the entire thing by hand. This does not apply to chess, evidently. Of course, I confidently explained this to him. »Prove it.«, he said. So I did. Do you want to know more?

Groupon sold my e-Mail address

born remark 2013-04-05

The idea behind groupon is to make it easy (and cheaper) for new customers to try out a service or product. The whole site really looks like racket but I used it some time ago. I have the common practice that I create an e-mail address for every single service I register to. So I used an e-mail address of the style "mymail-groupon@mydomain.tld" for it. Today I got an e-mail with the subject "Abmahnung Ihrer aussehender Rechnung über 262,00 Euro" (impolite german for "Reminder for a payment about 262 euros") from an debt collecting agency. Do you want to know more?

The Rainich Trick

rattle mathematics, remark 2013-04-03

Zariski's proof ((Oscar Zariski. A new proof of Hilbert's Nullstellensatz, Bulletin of the Ameican Mathematical Society Volume 53, Number 4 (1947), 362-368.)) of the Hilbert Nullstellensatz makes use of the ineffable Rabinowitch Trick ((J. L. Rabinowitsch, Zum Hilbertschen Nullstellensatz, Mathematische Annalen Volume 102, No. 1 (1929), 520.)) (check it out, that has got to be the shortest paper ever). But who is that awesome guy Rabinowitsch? I found out today, and the answer is basically in in this MO post: > Rainich was giving a lecture in which he made use of a clever trick which he had discovered. Someone in the audience indignantly interrupted him pointing out that this was the famous Rabinowitsch trick and berating Rainich for claiming to have discovered it. Without a word Rainich turned to the blackboard, picked up the chalk, and wrote RABINOWITSCH. He then put down the chalk, picked up an eraser and began erasing letters. When he was done what remained was RABINOWITSCH. He then went on with his lecture. Apparently, George Yuri Rainich is the mysterious stranger that went by the name of Rabinowitsch, which was his birthname ((Bruce P. Palka, Editor's Endnotes (May 2004), The American Mathematical Monthly 111 (5): 456–460)) ((Bruce P. Palka, Editor's Endnotes (December 2004). The American Mathematical Monthly 111 (10): 927–929)). I even updated the wikipedia page. Oh right, the reason this even caught my attention: Daniel R. Grayson has a really sweet, short proof of the Nullstellensatz, also using the Rainich Trick.