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Simple WordPress Update Script

rattle code, technology 2014-08-07

I need to update this wordpress install every once in a while. There are lots of bash scripts on the internet that perform this task, and they are complicated beyond reason. This is what I use:

function cfg {  
    grep $2 $1/wp-config.php | awk 'BEGIN {FS="[, )\x27]*"}; {print $3;}'
}

echo "> backing up database."
mysqldump --user=$(cfg $1 DB_USER) \
          --password=$(cfg $1 DB_PASSWORD)  \
          --host=$(cfg $1 DB_HOST)          \
          $(cfg $1 DB_NAME) > backup.database.sql

echo "> backing up website."
tar -cjf backup.files.bz2 $1
    
echo "> retrieving latest wordpress."
wget -q https://wordpress.org/latest.zip
unzip -qq latest.zip

echo "> updating wordpress."
rm -r $1/wp-includes $1/wp-admin
cp -r wordpress/* $1/

echo "> cleaning up."
rm -r wordpress
rm latest.zip

It takes a single argument, which is the name of your wordpress root directory. It backups your database to the file backup.database.sql and backups the files to backup.files.bz2, then it simply proceeds as described in the wordpress codex for updating manual. I do not see what all the fuzz is about.

Fresh Windows 8.1 Install on OEM Laptop

rattle technology

When you have a Laptop with Windows 8.1 preinstalled, then you will find yourself having a hard time installing a clean copy of Windows 8 on said Laptop. That, however, might be desirable for various reasons and so I am telling you how it's done. In my case, I am doing it with the firm intention to encrypt the system partition with TrueCrypt Setup 7.1a, which requires me to have an MBR rather than a GPT. There are probably ways to change this in-place, but there's really no point because I want a clean install of Windows anyway. (more…)

Member Variables in Python

rattle code 2014-07-27

Member variables in python are horrible. They are not visible in the layout of the class which is instantiated, but instead the __init__ function of a class creates certain member variables for the instance. I have never liked this about python, to be honest. For a recent project, I devised the following solution. Assume you would want this behaviour:

>>> class test(Base):
...     # Variables
...     number = 4
...     string = "hodor"
...     # Functions
...     def stringmult(self):
...         return self.number * self.string
...
>>> test().stringmult()
'hodorhodorhodorhodor'
>>> test(number=2).stringmult()
'hodorhodor'
>>> test(string="Na",number=8).stringmult() + " - Batman!"
'NaNaNaNaNaNaNaNa - Batman!'
>>> 
>>> test(end="Batman!")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ctypes.ArgumentError
>>>

In other words, any class that inherits from Base can be constructed with keyword arguments who must match exactly the correct class variables which you specify. This one does it:

from ctypes import ArgumentError
class Base(object):
    def __init__(self, **kwargs):
        # "given" is the list of keyword arguments passed to the constructor
        # of this object, "needed" is the list of class variables which belong to  
        # the base class of the object which is being created, which do not end 
        # with two underscores and which are not a function. Trust me, we do not 
        # want to meddle with those.
        given = list(kwargs.keys())
        needed = [attr for attr in dir(self.__class__) if attr[-2:] != '__' \
             and type(self.__class__.__dict__[attr])!=type(lambda:0) ]

        # Check if keyword arguments have been provided which are not among the
        # required arguments and throw an exception if so. Remove this check for
        # a less restrictive base class. I wouldn't recommend it.
        if not set(given) <= set(needed):
            raise ArgumentError()

        # First, initialize the attribute dictionary of the object being created
        # with a list of default values, indicated by the values of the class 
        # variables. Then, update the attribute dictionary again with the values
        # provided to this constructor.
        self.__dict__.update({k: self.__class__.__dict__[k] for k in needed})
        self.__dict__.update(kwargs)

I personally like this approach a lot and hereby dare you to tell me even a single reason not to do this, in the comments.

Why someone thought that sudoku might not be boring, while actually you should learn how to properly implement backtracking

rattle code, technology 2014-07-03

It causes me unspeakable agony to see that my post about why sudoku is boring is one of the most frequented posts in this blog, mostly because most of my readers clearly disagree with the title. I recently received an email titled "why sudoku is not all that boring" by an old friend, and he taunted me that the sudoku

S = [
  0, 0, 0, 0, 6, 0, 0, 8, 0,
  0, 2, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 1, 0, 0, 0, 0, 0, 0,
  0, 7, 0, 0, 0, 0, 1, 0, 2,
  5, 0, 0, 0, 3, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 0, 4, 0, 0,
  0, 0, 4, 2, 0, 1, 0, 0, 0,
  3, 0, 0, 7, 0, 0, 6, 0, 0,
  0, 0, 0, 0, 0, 0, 0, 5, 0 ]

would take my 5-minute hack of a backtracking algorithm

real    51m3.656s
user    50m32.260s
sys     0m2.084s

to solve. So, it seems like some sudokus are really hard, even for a computer, right? Wrong wrong wrong wrong wrong. Read how to implement backtracking properly.

Remote-Controll Android Phone via VNC

born technology 2014-06-14

Since everyone now uses TextSecure (no, really, you should switch too!), everything close to a TextSecure desktop client is not finished enough and I want to type messages from my computer (in the old SMS ages, I did this with MyPhoneExplorer), I decided to remote control my Android device. The setup is straight forward (if you already have root privileges on your device): * Install a VNC-Client for Windows (for example RealVNC) * Install a VNC-Server for Android (for example droid VNC server) * Go through the settings of the VNC-Server For some reason I cannot connect from my Computer to the Phone, but "Reverse Connection" works like a charm (don't forget to start the VNC Viewer in listening mode ... as ... some friend of mine did). Edit: And after a restart of my phone, the normal direction also works.

Statistics, and a neuroscientist to the rescue

shim mathematics, remark 2014-05-28

In the past weeks I've been visiting quite the number of jobs fairs, networking events, trainings on how to hunt for jobs and the like. I certainly learned a lot, albeit mostly things that are obvious after a moment of contemplation or come to you by common sense. Yet a simple reminder and a bit of practice are surely beneficial. High in demand are all these abstract skills we all have been told one too many times to include on your CV (complex and analytical thinking ...) and programming skills (although many employers seem to be happy to train on the job). What somehow fell of my radar and which came up more than once, is a basic knowledge of statistics. This leaves us in a bit of a pickle because most available material seems to fall into one of the two following categories: 1. Statistic for statisticians: Something we all have very actively decided against studying. All the proofs and constructions and endless excursions into theoretical concepts that haven't yet and maybe never will make their way into practice. Scientific exploration that is fun if and only if you have a thing for statistics. 2. Statistics for undergrads who don't even know if they need it, lectured by junior-professors or assistants who rather spend their time on research than on preparations: What you get is a incoherent bunch of powerpoint slides that seem to live more through examples than concise explanations and miss out on the most important part, namely a self-contained overview over available methods. To the rescue comes Arnaud Delorme, a computational neuroscientist from the University San Diego. His paper on statistical methods does basically everything you want on 23 pages: A quick recap of the necessary definition, a clean-cut overview over the most common methods and a short concise explanation for each of them with just the right amount of theoretical background and a short demonstrating example. Sure, towards the end it can be a bit tiresome to go through method after method and you won't want to read it front to back in one go. Of course I also can't guarantee for its exhaustiveness, but it seems like we have a winner when it comes to ratio of usefulness over required time-investment.

Offline Maps

rattle technology 2014-05-24

It used to be a problem to get good route planning on your smartphone when you are outside the country, because the roaming fees could plunge any McKinsey employee into bankrupcy when using Google Maps, which is only able to cache small map sections and basically has no way of telling you what is cached and what isn't. Rejoice! The OSMAND project provides an open maps and route planning solution which allows you to download all kinds of maps for offline use. I personally like the Android App even better than Google Maps: It's clearly for power users, there is much more to configure and you have more control. There is always an obvious argument for choosing another option over the kraken, but the option to download maps for offline use has to be the main reason why this is awesome. The entire Open Street Map project (see also the German version) seems to be a cool project which is worth contributing to, even if it's just pointing out a house number here and there.

Migrating from Opera 12 to Firefox

rattle technology

Opera was updated. They messed up. Let's not talk about this any more. Let's talk about how to make Firefox your new Opera 12. To get the elephant out of the room right away: Yes, you guessed right, I did not switch to Chrome because I am scared of Google harvesting all my data and browsing habits. So that leaves only Firefox, and I think that they did good with the recent releases. We probably can not get back everything we miss from Opera 12 times, but some of it is possible, and even better in Firefox. First of all, Firefox has bookmarks and you can import them from an HTML export of your old bookmarks. For everything else, continue reading. If you are still missing a feature, feel free to post it with or without solution - in the latter case, I will try and solve it myself. (more…)

Irreducible Highest Weight Vectors

rattle mathematics 2014-05-23

Let $G$ be an affine, connected, reductive group and $X$ a $G$-module. Choose a maximal torus $T\subseteq G$, a Borel $B\subseteq G$ containing $T$ and let $U$ be the unipotent radical of $B$. Denote by the character group of $T$. Let $\Lambda\subseteq\mathbb{X}$ be the set of dominant weights of $G$ with respect to these choices. We can decompose the graded coordinate ring $\mathbb{C}[X]=\bigoplus_{\lambda\in\Lambda} V_{(\lambda)}$ into its isotypic components $V_{(\lambda)}$ of weight $\lambda$. Let \[ \Lambda_X=\{ \lambda\in\Lambda \mid V_{(\lambda)}\ne\{0\}\} \] be the set of weights that occur in $\mathbb{C}[X]$. Let $V_{(\lambda)}\cong V_\lambda^{\oplus n_\lambda}$, where $V_\lambda$ is the irreducible module of highest weight $\lambda$. Each $V_\lambda$ has a highest weight vector which is unique up to scaling - let $f_{\lambda 1}, \ldots, f_{\lambda n_\lambda}\in V_{(\lambda)}$ be linearly independent highest weight vectors. Claim. *For each $1\le k\le n_\lambda$, if the function $f:=f_{\lambda k}\in\mathbb{C}[X]$ is reducible, then there exist weights $\lambda_1,\ldots,\lambda_r\in\Lambda_X$ such that $\lambda$ is an $\mathbb N$-linear combination of the $\lambda_i$.* Indeed, about a year ago this statement was completely unclear to me. However, it's actually not that hard to see and I felt like sharing my proof. (more…)

A determinant for reductive groups

rattle mathematics 2014-05-17

For the group $G=\mathrm{GL}_n(\mathbb{K})$ of invertible matrices over any field, there is the well-known determinant character $\det:G\to\mathbb{K}^\times$ which, well, maps any matrix to its determinant. It has the property that \[ [G,G]=\mathrm{SL}_n(\mathbb{K})=\{ g\in G \mid \det(g)=1 \}, \] where $[G,G]$ denotes the derived subgroup of $G$. In more geometric terms, $[G,G]$ is the vanishing of the regular function $\det-1$ on $G$. Because I find it rather cute, I will show that you can find a similar function for all linear, reductive groups. (more…)

Das Master Theorem

rattle mathematics 2014-05-06

Ich habe letzte Woche versucht, für einige Studenten das Master Theorem zu beweisen. Das ist geringfügig daneben gegangen, deswegen habe ich eine korrigierte Version des Beweises erstellt. Ich frage mich nun aber schon, wie allgemein man das eigentlich machen sollte. Grundsätzlich könnte man sich für eine Laufzeitfunktion $T:\mathbb N\to\mathbb N$ ja Rekurrenzgleichungen der Form $T = \alpha \circ T \circ \beta$ ansehen, wobei in meinem Fall $\beta(n)=n/b$ und $\alpha(n)=a\cdot n + f(n)$ ist. Ich habe leider keine Zeit, mir dazu mehr Gedanken zu machen.

Make VIM work in Cygwin

rattle technology 2014-05-01

Well. In case you have not stumbled across the corresponding StackOverflow post, and if you have always wondered why vim does not work properly in cygwin, just

[rattle@ALICE:~]$ cat .vimrc
set nocompatible
set backspace=indent,eol,start

and your worries will be over.

Multiple Dropbox Accounts on one computer – a Batch script to automate the process

born technology 2014-04-24

A lot of people are in the situation where they want to use more than one Dropbox account on one (windows) machine (for whatever reason). The default way of doing this is the following: * create a new local user account * log in as that user and install Dropbox * log back in as the default user and use something like psexec to execute the installed Dropbox as the other user account while being logged in as default user To automate this process, I wrote the following script that also takes care of cosmetics like "hiding the newly created user from the login screen". Do you want to know more?