Als großer Befürworter von <a href="http://de.wikipedia.org/wiki/Palatino" target="_blank">Palatino</a>-Schriftarten ((insbesondere auch <b>mathpazo</b> für mathematische Texte)) möchte ich natürlich auch meine Briefe so verfassen. Wem das nicht passt, der kann ... trotzdem weiterlesen! Wesentlich wichtiger war mir für diesen Brief nämlich, dass die Adresse des Empfängers bei korrekter Faltung in einem Fensterumschlags sichtbar ist. Das <a href="/wp-content/uploads/2012/04/letter.pdf" target="_blank">sieht dann etwa so aus</a>. <a href="https://blag.nullteilerfrei.de/2012/04/12/schone-din-konforme-briefe-in-latex/#more-736" class="more-link">Wollen Sie den Code sehen?</a>
Let's say you have a vector space $V$ and a vector space $W$ over the same field $k$. Then, according to a huge pile of books on representation theory I read, there is an <i>obvious</i> isomorphism $V^\ast\otimes_k W \cong \mathrm{Hom}_k(V,W)$, where $V^\ast=\mathrm{Hom}_k(V,k)$. I concur, it's not hard to write down, but then <b>why</b> don't they just write it down? It is given by
\[
\begin{array}{rcl}
\phi: V^\ast\otimes_k W &\longrightarrow& \mathrm{Hom}_k(V,W) \\
f\otimes w &\longmapsto& (v\mapsto f(v)w),
\end{array}\]
when we assume $W$ to be finite-dimensional. <a href="https://blag.nullteilerfrei.de/2012/04/12/the-obvious-tensorhom-identification/#more-687" class="more-link">Do you want to see the proof?</a>
Ich befand mich vor nicht allzulanger Zeit in der unerquicklichen Lage, dass mein sage und schreibe sieben Jahre altes <a href="http://de.wikipedia.org/wiki/ThinkPad" target="_blank">ThinkPad</a> so langsam den Geist aufgab. Meiner Meinung nach sind ThinkPads immer noch das Mittel der Wahl, auch wenn inzwischen Lenovo draufsteht. Ein Kommolitone empfahl mir dazu <a href="http://www.nbwn.de/" target="_blank">Notebooks wie Neu</a>: Dort werden ThinkPads verkauft, die mal irgendwann auf irgendeiner Messe ausgestellt worden sind und damit formal als Gebrauchtware gelten. Ich war zunächst skeptisch, doch gab es mein Wunschmodel dort rund 30% günstiger, also wurde das gute Stück einfach direkt mal gekauft. Ich habe es jetzt einige Wochen und kann nur sagen, ich bin <b>rundum zufrieden</b>. Das Gerät ist <i>wirklich</i> wie neu.
I am currently working through the book on <a href="http://books.google.de/books/about/Young_Tableaux.html?id=cYA_RpBLJUkC&redir_esc=y">Young Tableaux</a> by Fulton, and I find it a very nice read - in a prose ((Attention Nikolai: Do <b>not</b> touch this book.)) kind of way. As you might notice from the general sound of it, I am getting into representation theory. However, this book is more about the combinatorical aspects of the field. Since combinatorics is a very hands-on kind of math, I really think I should do a certain amount of exercises. I am only skimming through the book since ultimately, I want to get back to abstract nonsense really bad, but I will write down my solutions for any exercise I do ((I know that the book already contains <em>"solutions"</em>, but I'd rather call them <em>"hints"</em>.)) . <a href="https://blag.nullteilerfrei.de/2012/04/03/young-tableaux/#more-612" class="more-link">Do you want to know more?</a>
Just a checklist for programming the microncontroller Ralf gave me yesterday ((Also check out <a href="http://www.mikrocontroller.net/articles/AVR_Eclipse">this useful article</a>))
* you need a functional eclipse installation
* Install WinAVR and be sure that it is in the `PATH` by executing `avr-gcc` from a command prompt
* Install the AVR-Interface into eclipse via `Help` → `Install New Software` → `Add`. Then paste the following link in the URL Box:
```text
http://avr-eclipse.sourceforge.net/updatesite/
```
* When I create a new project, I need to adjust the following settings in the project properties:
* `AVR` → `AVRDude` `Programmer` click on `New`, Name: `USBASP`, Programmer Hardware (`-c`) `USBasp, http://www.fischl.de/usbasp/`
* `AVR` → `AVRDude`, `Advance` be sure the check `Disable device signature check`
* `AVR` → Target Hardware `MCU Type` select `ATmega168` and set the `MCU Clock Frequency` to `12000000` (that's $12\cdot10^6$)
* `C/C++-Build` → Settings unter `Tool Settings` check `Generate HEX file for Flash memory`
* `C/C++-Build` → Settings unter `Tool Settings`, `AVR Compiler` → `Optimization` set the `Optimization Level` to `Size Optimizations (-Os)`.
This article adresses the following problem: Assuming you have some amount of data, let's say 20 GB, on your local machine at home, and you would like to synchronize this data with a remote server. You are a security aware person and your local hard drive is encrypted. Therefore, it would make no sense to just upload this data unencryptedy to an unencrypted remote server you eventually don't even really trust. We suggest the following solution to this problem (assuming you work in a Win7 environment or something like that): Instead of the data itself, we will upload a True Crypt file container instead. Then we use Dokan to mount the remote drive as a local drive. The file container on this ''local drive'' is then mounted via True Crypt as a drive. Now you can use any local synchronization tool of your choice and dismount everything again. Usage of all this different software can be simplified by using AutoHotkey. <a href="https://blag.nullteilerfrei.de/2012/03/25/truesync/#more-314" class="more-link">Do you want to know more?</a>
In the recent weeks, we have acquired the phony habit of customizing our Windows desktop PC's. The following is my checklist for making a Windows PC more pretty.
## Making Windows Themable
You go and download the universal theme patcher:
* <a href="http://deepxw.blogspot.de/2009/01/download-latest-version.html#UniversalThemePatcher" target="_blank">Universal Theme Patcher Homepage</a> (<a href="http://deepxw.blogspot.de/" target="_blank">Author's Blog</a>)
* <a href="/wp-content/uploads/2012/03/UniversalThemePatcher_20090409.zip" target="_blank">Universal Theme Patcher on nullteilerfrei</a>
Then, you click it. You can find a ton of themes on <a href="http://www.deviantart.com" target="_blank">deviant art</a>, but I'd strongly advise against overly dark themes, it really does not make for a healthy working environment.
## The Logon and Boot Screen
To customize the windows login screen to look really nice, we have to do several things.
* To change the <b>background image</b>, you simply use the Tweaks Logon Changer:
* <a href="http://tweaks.com/software/tweakslogon/" target="_blank">Tweaks Logon Changer Homepage</a>
* <a href="/wp-content/uploads/2012/03/tweakslogon.zip" target="_Blank">Tweaks Logon Changer on nullteilerfrei</a>
* To remove the little <b>branding logo</b> on the bottom of the login screen, you open the file
```text
%SystemRoot%\Branding\Basebrd\basebrd.dll
```
in a resource editor of your choice ((We recommend either <a href="http://anolis.codeplex.com/releases/view/32286" target="_blank">resourcer</a> or <a href="http://www.angusj.com/resourcehacker/" target="_blank">resource hacker</a>.)) and simply delete the corresponding resource bitmaps. Note that some of the bitmap resources are not used for the logon screen but for other dialogs, such as the shut down menu that appears when pressing ALT+F4 on the desktop.
* If you have a <b>fingerprint reader</b> and you are annoyed by the blue Fingerprint icon, you can change these icons by replacing the bitmaps in the file
```text
%SystemRoot%\System32\BioCredProv.dll
```
## The Boot Screen
To change the Windows boot screen, best use the Windows 7 Boot Updater:
* <a href="http://www.coderforlife.com/projects/win7boot/" target="_blank">Windows 7 Boot Updater Homepage</a>
* <a href="/wp-content/uploads/2012/03/Win7BootUpdater.exe" target="_blank">Windows 7 Boot Updater on nullteilerfrei</a>
## The Start Orb
For changing the start Orb in Windows, I strongly recommend using the Start Orbz Studio;
* <a href="http://blizo.deviantart.com/art/StartOrbz-v3-1-a-155061270" target="_blank">StartOrbz Studio on deviant art</a>
* <a href="/wp-content/uploads/2012/03/startorbz_v3_1_a_by_blizo-d2kbi1i.rar" target="_blank">StartOrbz Studio on nullteilerfrei</a>
## The Wallpaper
Seriously? I really like <a href="http://alpha.wallhaven.cc/" target="_blank">wallhaven</a>, but there are most literally a million wallpaper archive sites out there.
Why would anyone want to use Windows 2008 R2 Server as a workstation? The main arguments in <i>my</i> case are the superior <b>firewall</b> and <b>user account control</b>. Now, if you want to do the same, you can go to <a href="http://win2008r2workstation.com/" target="_blank">win2008r2workstation.com</a> and get a really detailed howto with screenshots - or you can read this post for a really short checklist, something I prefer to have for future installs of the same variety. <a href="https://blag.nullteilerfrei.de/2012/03/22/turning-windows-2008-r2-into-a-workstation/#more-495" class="more-link">Do you want to know more?</a>
In the process of doing some windows customization, Chuck shot his Windows dead. Hence, we needed a USB stick to boot <a href="http://grml.org/" target="_blank">Grml</a>. It's quite easy to make a USB stick bootable in Windows, and here's the short version: I will assume that your USB stick is drive <b>U:</b>. Use the command-line tool <b>diskpart</b> and use the command <b>list disk</b> to find your USB stick (check the size). Then, enter:
```bash
select disk <usb stick number>
clean
create partition primary
select partition=1
active
format fs=ntfs quick label=”overdrive”
assign
```
and exit the <b>diskpart</b> utility. Finally, use
```bash
bootsect /nt60 U:
xcopy <image>:\*.* U:\*.* /S /E /F
```
to first make the stick bootable and then copy all data to the stick, where <b>image</b> is a directory where the files from your ISO reside. If you do not have the <b>bootsect</b> utility for some reason, grab it from a friend who has Windows 7.
After a couple of tests, it turns out that the very simple
```C
#include <limits.h>
inline void memzap(void *dest, unsigned long count) {
asm( "cld"
# if ULONG_MAX == 0xffffffff
"\n" "andl $3, %%ecx"
"\n" "rep stosb"
"\n" "movl %%ebx, %%ecx"
"\n" "shrl $2, %%ecx"
"\n" "rep stosl"
# else
"\n" "andq $7, %%rcx"
"\n" "rep stosb"
"\n" "movq %%rbx, %%rcx"
"\n" "shrq $3, %%rcx"
"\n" "rep stosq"
# endif
: "=c" (count), "=D" (dest), "=b" (count)
: "c" (count), "D" (dest), "b" (count), "a" (0)
);
}
```
is the fastest way to zero out a large block of memory, which is not very surprising. It is about 4 to 5 times faster than `memset` and about as fast as `new []`, if I can trust @tobi on that matter. I tried using MMX registers, but anything that involves `actually` looping over the memory region will be about as fast as `memset`. The only way to get a bit of speed is using the `rep` opcode.
<b>Tiny Edit:</b> The above code is much more safe to compile on both 64 and 32 bit computers.
<a href="http://www.truecrypt.org/">TrueCrypt</a> is the tool of choice to encrypt your computer hard drives, and under windows it offers the option to encrypt the system drive on the fly, which is very comfortable. As you might guess, this could also go terribly wrong, which is why TrueCrypt forces you to create a <a href="http://www.truecrypt.org/docs/?s=rescue-disk">rescue disk</a> ISO, which has saved me a lot of trouble in the past. However, by default, TrueCrypt does not let you encrypt your system drive before you have <b>actually</b> burned that image to a <b>real</b> CD, and that, on the other hand, is quite annoying in a day and age where many notebooks no longer have an optical drive. What few people know - this check can be turned off by executing
```bash
"TrueCrypt Format.exe" /noisocheck
```
If you don't believe me, try it yourself or <a href="http://www.truecrypt.org/docs/?s=command-line-usage" target="_blank">check out their documentation</a>.
For reasons I have not yet been able to figure out, @tobi is making me implement a couple of very rudimentary routines in x86 GCC inline assembler because he wants them faster than possible for mere mortal C. The first was a routine to calculate $\lfloor\log_2(n)\rfloor$ for $n\in\mathbb{N}$ and the second one was to zero out a large block of memory. For instance,
```c
unsigned inline log2int(unsigned x) {
unsigned l;
asm("bsrl %1, %0" : "=r" (l) : "r" (x));
return ( 1 << l == x ) ? l : l + 1;
}
```
is about 50 times faster than the C-native Version
```c
unsigned inline log2int(unsigned x) {
unsigned l = 0;
while(x > (1<<l)) l++;
return l;
}
```
even after optimization. For some reason, I found it tricky to google up the official intel x86 opcode reference ((<a href="http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-2a-manual.pdf" target="_blank">Opcode Reference Part 1</a>)) ((<a href="http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-2b-manual.pdf" target="_blank">Opcode Reference Part 2</a>)), so I am linking these here.
I am writing this blag post from the <a href="http://www.math-conf.uni-hannover.de/spp1489/index.php" target="_blank">second annual meeting of the DFG priority programme SPP1489</a> (algorithmic and experimental methods in algebra, geometry and number theory). Apart from having a lot of fun, I am catching up on the recent developments in open-source computer algebra software. <a href="https://blag.nullteilerfrei.de/2012/02/29/open-source-computeralgebra-2012/#more-422" class="more-link">Do you want to know more?</a>