# How to undo a commit in git

Really throw away everything (all changes!) from the last commit:

git reset --hard HEAD~1


Delete the commit, but preserve all changes:

git reset --soft HEAD~1


For more details and explanations, read this excellent answer by Ryan Lundy on stackoverflow.

# Other settings for “non-scientific” texts in LaTeX

Figures that have no numbers, but only text in the captions:

\usepackage{caption}
\captionsetup[figure]{labelformat=empty,textfont=footnotesize}
\renewcommand{\thefigure}{}


No indentation at the beginning of a paragraph, but a bigger separation space between paragraphs:

\setlength\parindent{0pt}


Header lines that contain only page number and chapter, not the section:

\usepackage{scrlayer-scrpage}
\clearpairofpagestyles
\automark[chapter]{chapter}


# LaTeX package “wrapfig”

LaTeX is all nice and fancy if you write technical texts, where the pictures are floating in the text (mostly at the top and/or bottom of pages) and you reference them with numbers. But as I do all sorts of things with LaTeX, sometimes I want more “fun” texts which have pictures somewhere in the pages and text flowing around them.

For this purpose, I have now discovered the package wrapfig:

\usepackage{wrapfig}


You can include a picture like this (this one floats left of the text with a width of 7em):

\begin{wrapfigure}{l}{7em}
\centering
\includegraphics[width=\linewidth]{AuthorOfArticle.png}
\end{wrapfigure}


You can control some of the appearance with different settings in the preamble (see the documentation at CTAN), e.g.,

\intextsep0.5ex


# Docker cleanup

Delete all containers

docker rm $(docker container ls -a -q) Delete all unnamed images docker rmi$(docker image ls | grep "<none>" | tr -s ' ' | cut -d ' '  -f 3)


docker image ls lists all images,
grep "<none>" selects all that have the tag (or repository! or part of name!) “<none>” ,
tr -s ' ' merges sequences of spaces to a single space,
cut -d ' ' -f 3 splits each line at the space and gives the third column (the image id).
The list of ids is then passed on to docker rmi to be deleted.

# How to get WiFi running on Suse Leap 42.3 (Broadcom driver)

After the update from Suse Leap 42.2 to Suse Leap 42.3, my Wifi stopped working. Which is kind of bad, because I need internet to figure out what is wrong…

This was the situation right after the update, when it was not working:

> lspci -nnk | grep -A 3 "Network"
04:00.0 Network controller [0280]: Broadcom Corporation BCM43142 802.11b/g/n [14e4:4365] (rev 01)
Subsystem: Hewlett-Packard Company Device [103c:804a]
Kernel driver in use: bcma-pci-bridge
Kernel modules: bcma

> hwinfo --short
network:
eth0                 Realtek RTL8101/2/6E PCI Express Fast/Gigabit Ethernet controller
network interface:
eth0                 Ethernet network interface
lo                   Loopback network interface

> iwconfig
lo        no wireless extensions.
eth0      no wireless extensions.

> lsmod | grep "wl"


No WiFi to be seen!

So now this is what I did:

1. Remove the old driver:
> rpm -e broadcom-wl broadcom-wl-kmp-default

2. Find out my exact kernel version (the last part is the part we need, i.e., “default”):
> uname -r
4.4.104-39-default

3. Add the Packman repository to my repositories:
> zypper addrepo http://packman.inode.at/suse/openSUSE_Leap_42.3/ packman

4. Install the drivers, paying attention to my kernel type (…-“default”):
> zypper install broadcom-wl-kmp-default broadcom-wl


You can also download the rpm by hand and install it. In that case, you need to pay attention to the full kernel number. Meaning, for my kernel 4.4.104-39, I should install the driver from broadcom-wl-kmp-default-6.30.223.271_k4.4.49_19-3.6.x86_64.rpm where the numbers after the k match exactly. Using Packman does that for you.

Another issue I had with manual installation was missing keys. At least my configuration forces a valid PGP key and aborts if no key is in the key list. And I didn’t have a key for the downloaded rpms. It is possible to tell rpm to install the packages without checking the key (option --nosignature), but that did not properly install the package (without error messages, of course). When installing with zypper it looks for the key itself and you don’t have to worry.

5. I rebuilt the loaded modules list and then restarted, but I am not sure it is necessary:
> mkinitrd


Finally, the outputs of the above commands are (for reference, the next time it breaks):

> lspci -nnk | grep -A 3 "Network"
04:00.0 Network controller [0280]: Broadcom Corporation BCM43142 802.11b/g/n [14e4:4365] (rev 01)
Subsystem: Hewlett-Packard Company Device [103c:804a]
Kernel driver in use: wl
Kernel modules: bcma, wl

> hwinfo --short
network:
eth0                 Realtek RTL8101/2/6E PCI Express Fast/Gigabit Ethernet controller

network interface:
wlan0                WLAN network interface
eth0                 Ethernet network interface
lo                   Loopback network interface

> iwconfig
lo        no wireless extensions.
wlan0     IEEE 802.11abg  ESSID:"..."
Mode:Managed  Frequency:2.412 GHz  Access Point: ...
Bit Rate=65 Mb/s   Tx-Power=200 dBm
Retry short limit:7   RTS thr:off   Fragment thr:off
Encryption key:off
Power Management:off
Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
Tx excessive retries:0  Invalid misc:0   Missed beacon:0
eth0      no wireless extensions.

> lsmod | grep "wl"
wl                   6451200  0
cfg80211              610304  1 wl


And it only took all afternoon … sometimes I hate Linux 🙁

# Inkscape Basics (because I forgot what I knew a week ago)

Resize Inkscape svg canvas to it’s content
Go to File -> Document Properties -> Page
Resize page to drawing or selection

Add guides helps with alignment etc.
Just click ruler and drag down from top, left or even top/left for diagnonal guide

Setup/Change snapping when moving objects around
Go to File -> Document Properties -> Snap

Change color of object
Go to Object -> Fill and stroke (Shift+Ctrl+F)

Posted in Mac

# Get version of a Java package (in Java)

It’s easy!

String version = myObject.getClass()
.getPackage()
.getImplementationVersion();


Where it comes from…? I think from the MANIFESTO in the jar file.

# Overlays with Code Listings

You cannot include a lstlisting (package listings) in a only or visible command in LaTeX beamer. BUT you can define the listing beforehand and then include that inside the only or visible!

Example (from slides about recursion in Java):

\defverbatim{\Lst}{
\begin{lstlisting}
public int fakultaet(int n) {
if ( n == 1 ) {
return 1;
} else {
return n * fakultaet( n-1 ) ;
}
}
\end{lstlisting}
}

\begin{frame}[fragile]
\frametitle{Aufgabe: Fakultät von $n$}

Definition:
\begin{itemize}
\item \lstinline{fakultaet( 1 ) = 1}
\item \lstinline{fakultaet( n ) = n * fakultaet( n-1 ) }
\end{itemize}

\bigskip

Java Code:
\visible<2|handout:0>{\Lst}

\end{frame}


# Setting computer time from the internet [hacky way]

Most of my pool computers show the wrong time and most of them are different. Just for fun, here are the times shown by those running at the moment of the poll:

8:36 (2x), 8:40, 9:36 (2x), 10:35, 10:36 (3x), 10:39 (6x), 11:36 (2x), 11:40

I assume it is the result of setting the time wrong in the installation and then a few semesters of trying to fix some of them (those running at the moment, the first three rows, until the admin was bored, a single one now and then, …), adjusting to daylight savings time or forgetting it and so on.

So this is what I tried to get them back on track (courtesy of AskUbuntu.com):

sudo date -s "\$(wget -qSO- --max-redirect=0 google.com 2>&1 | grep Date: | cut -d' ' -f5-8)Z"


The line first gets a random web page (here google.com) and prints the header of the HTTP response, e.g.,:

  HTTP/1.1 302 Found
Cache-Control: private
Content-Type: text/html; charset=UTF-8
Referrer-Policy: no-referrer
Content-Length: 266
Date: Thu, 14 Dec 2017 10:46:49 GMT


The line then retrieves the part of the response with the date using grep. It splits the line with the date at spaces with cut -d ' ' and uses the parts 5 to 8. In this line, part 4 is the day of the week, part 3 is the text Date: and parts 1-2 are empty because of the leading spaces. So using parts 5 to 8 results in a date and time in a format that the tool date can understand. Before passing the time on to date, the letter Z is appended. This Z stands for UTC, meaning the time zone set on the computer will be taken into account.

So the line after evaluating wget, grep and cut for the example page we got will be:

sudo date -s "14 Dec 2017 10:46:49Z"


The option -s sets the date to the specified value. So if the request ran in a reasonable time, we should have a reasonably accurate time set for the computer.

PS: Yes, I know that there is such a thing as NTP and I know that time synchronization is not a problem that you need to hack on your own. But this version is much more freaky and cool!! [Also NTP and the university firewall don’t seem to be friends]

# Discontinuous x axis with pgfplots

Having a discontinuous y axis is common and Stackoverflow has a few solutions for that. I wanted an x axis with a gap (values 0-10 plus value 20). So this is what I did.

I create an axis from 0 to 12 and give 12 the label “20”. I add an extra tick on the x-axis at about halfway between 10 and “12”, where I want the gap and make it thick and white – basically I want a break in the axis. Then over that break I draw the “label” of this tick, which is two vertical lines at an angle, symbolizing the discontinuity. The relevant part of the style:

xmin=0,
xmax=12.5,
xticklabels={0, 2, 4, 6, 8, 10, 20},
extra x ticks={11.1},
extra x tick style={grid=none, tick style={white, very thick}, tick label style={xshift=0cm,yshift=.50cm, rotate=-20}},
extra x tick label={\color{black}{/\!\!/}},


And then I add the data with x-values 20 at x-coordinate “12”:

\addplot coordinates {
(0, 43.3) (1, 43.2) (2, 43.3) (3, 42.9) (4, 42.1) (5, 41.4)
(6, 41.2) (7, 41.7) (8, 41.7) (9, 42.1) (10, 42.1) };
\pgfplotsset{cycle list shift=-1}
\addplot coordinates { (12, 43.8) };
\draw[dotted] (axis cs:10, 42.1) -- (axis cs:12, 43.8);


Adding the last point separately from the rest of the data serves the purpose that I can draw the dotted line by hand. cycle list shift=-1 causes the new “plot” to have the same style as the previous. There might be a way of doing this, but this works.

Hat tip: Stackoverflow, but I currently cannot find the question(s) and answer(s) that helped me solve this. Still, thank you, anonymous people.