Commands that save your Sanity No 1

:w !sudo tee %

overwrites a file that you don't have permission to write to but edited with vim nonetheless.

Replacing parts of your Macbook Air

I had a need for replacing my Macbook Air's top case and heard it was insanely difficult beforehand. This was definitely not the case (despite some 80 odd screws of over ten different sizes) thanks to this guide. So if you need to do it yourself don't fret, trust ifixit!

On a side note: I was thoroughly surprised to see how thought out and beautiful the inside of the Macbook Air was. I'm still unsure what to think of it but they even introduced blinds in black varnish look that have no other purpose but optical ones. Overall it is really an impressive piece of craftsmenship though not necessarily all by apple (e.g. i was most impressed with size of the mainboard)

Mac OS X Skype Tab switch shortcuts

Since I had a hard time finding out what the command is for switching the tab in the conversation window, let it be known that it is Command+Shift+left/right Arrow

big/small delimiters fontsize

Ok this is old news but i am sick of googling it now.

Delimiters can be sized manually (i.e. not with \left \right) with \big \Big \bigg \Bigg. The sizing of these is adjusted (to the better when loading the amsmath package)

Non delimiters (and this includes Integrals and Sums) can be resized with \tiny
\scriptsize
\footnotesize
\small
\normalsize (default)
\large
\Large
\LARGE
\huge
\Huge

overlapping/embracing braces

I recently had trouble trying to tex this:



If you have some experience with latex you see the trouble with the overlapping here. It took a while and it's a load of patchwork, but it works beautifully.

\contraction{a_{n'} + \makebox[0pt][l]{$
\displaystyle{\cuntraction{\phantom{a_r(k) +
\overline\psi(x) \gamma^\mu \psi(x) A_\mu(x)}}}$}
a_r(k) + \overline\psi(x)} \gamma^\mu \makebox[0pt][l]
{$\displaystyle{\contraction{\phantom{\psi(x)
A_\mu(x) a^{+}_{n}}}}$} \psi(x) A_\mu(x) a^{+}_{n}
\ket{0}
It looks like this:


contraction was defined here and cuntraction is the same with an overbrace instead. To understand all ingredients review this pdf

The main idea is that makebox collapses the bounding box that latex uses to position items on a page without touching the content, so the under/overbrace will be displayed and dimensioned according to the lenght of its argument, which in turn won't be displayed because it's hidden via phantom. Since the bounding box is collapsed the following text will start as if there hadn't been any box.

PS:
I thought the above was complicated. Well i stand corrected, the following is plain ridiculous:

QFT/QED weirdness

I am latexing QED and QFT at the moment and some of it is just price less, so I thought I'd share to save you some time.

First up is the Feynman slash, i first tried hacking something up myself:
\renewcommand{\slash}{\hskip -3pt\not\hskip -2pt}
this however has a few issues because it would need to be skipped differently for different letters, the line width of the slash was never quite right and it's too low.

After some more googling i found the slashed package. Which looks better:

Next up was a contraction symbolized by an underbracket. This functionality is provided by the mathtools package except that it looked to big for the fonts i use. Fortunately there are some optional arguments that fix that issue.

\newcommand{\contraction}[1]{\underbracket[0.2ex][0.5ex]{#1}}



And now comes my favourite: My Quantum field theory professor decided to make up a nonstandard way of being undecided about whether we are in a continous or discrete space and just superimposed a sum and an integral instead of using common sense and Dirac measures.
Marvel at this beauty:
\newcommand{\Sunt}[1]{\hskip5pt\int\hskip -15pt \sum_{#1}\kern 2pt}
\newcommand{\sunt}{\hskip3pt\int\hskip -10pt \sum}
Of course capital is for Displaystyle.

Quabla/D'alembert & Laplace in Latex

Forgot to post it in English: The short story is try the Operators defined below if you have a need for the differential operators. I'd be glad to hear someone suggesting something even better.


Ich habe mal wieder den Quabla und den Laplace gebraucht und bisher verwendete ich immer \Box  und \bigtriangleup.
Das sieht so aus:  
Ich bin persönlich nicht wahnsinnig anspruchsvoll was das Design angeht, aber heute fand ichs einfach zu hässlich und hab nach etwas ausgiebigerer, erfolgloser Suche  (GINMF) beschlossen einfach selbst einen zu bauen. Zunächst sind mir die Operatoren einfach etwas zu groß, vor allem bei kleinen lateinischen Buchstaben und desweiteren finde ich dass gerade bei dem \phi das ganze auch etwas zu hoch sitzt.
Nach einem ausgiebigen Buchstudium musste ich feststellen, dass das jeder Autor anders löst und die meisten schauen nur OK aus, der Rest noch schlechter. Auffällig dabei ist, das drei verschiedene Zeichen im Gebrauch sind für das Laplace, \bigtriangleup, \Delta und eins, was ich nicht identifizieren konnte, vermutlich eine italizierte Version von \Delta. Das ist natürlich alles eine Frage des Geschmacks und der Konvention für Vektoren im jeweiligen Text; ich präferiere auch nach dem Vergleich noch \bigtriangleup.
Nach einigem rumprobieren musste ich feststellen, dass tieferstellen gerade bei Buchstaben wie dem A, das eine relativ definierte Baseline hat, nicht toll aussieht und habe letztlich nur alles etwas kleiner gemacht. Das Problem dabei ist, dass \scriptsize für den Quabla und \footnotesize Laplace optimal wären in meinen Augen, es aber inkonsistent aussieht, wenn die in verschiedenen Größen in der gleichen Gleichung auftauchen.

 Ich würde daher vorschlagen, wenn beide in einer Gleichung vorkommen \footnotesize zu nutzen und ansonsten das jeweils optimale wählen. Ist zwar auch inkonsistent, aber das kleinste Übel in meinen Augen. Ergebnis:


\newcommand{\Lapl}{\hbox{\footnotesize{$\bigtriangleup$}}}
\newcommand{\Quabla}{\hbox{\footnotesize{$\Box$}}}
\newcommand{\quabla}{\hbox{\scriptsize{$\Box$}}}

Das Endresultat sieht so aus: