## Installing Sumatra 0.6-dev in Ubuntu 13.10

Sumatra is a great tool for reproducibility and provenance when you are running numerical simulations. Keeping your work reproducible ensures that you and others will be able to check your results at a later time, while provenance is to keep track of where your results came from in the first place.

I won’t get into details about using Sumatra in this post, as its documentation is quite good at describing that already.

## Computational Physics members

If you are a member of the Computational Physics group and have access to the computing cluster, Smaug, you don’t have to install anything. Just ssh into our dedicated Sumatra machine, named bender, and run your jobs from there. In the future, all machines will support Sumatra, but for now, we only have one dedicated machine for this task:

ssh bender

Otherwise, or if you want it on your own machine, you will have to install it manually. This is done by cloning the repository and running the setup.py file. This will install Sumatra with all dependencies:

hg clone https://bitbucket.org/apdavison/sumatra
cd sumatra
python setup.py install --user

Adding –user to the final command ensures that all packages are installed to your home directory, under .local/lib, so that  you don’t have to install with sudo privileges, and it makes it a bit easier to remove the package if you don’t want to keep it.

We also need the GitPython and PyYAML modules, which you may install using apt-get:

sudo apt-get install python-git python-yaml

And that’s it! You should now be able to run your projects with Sumatra.

## Recent commit causes Qt3D to fail compilation

A recent commit pushed to the Qt3D repository breaks building Qt3D against Qt version 5.2 and older with the following error message:

painting\qglpainter.cpp:2348:29: error: 'class QOpenGLFunctions' has no member named 'glReadPixels'

Thankfully, rolling back to an older commit still works. Just supply the following command after pulling the Qt3D repository:

git checkout d3338a9 -b older_version

This should enable you to compile Qt3D for Qt5.2 and earlier.

## Focusrite Scarlett 2i2 working flawlessly on Ubuntu with JACK

I needed a new sound card for Ubuntu that would allow me to do some recording and playback easily. After a bit of searching and testing, I figured I would go with the Focusrite Scarlett 2i2, which is a USB sound card with 2 XLR + jack inputs, stereo monitor output and a headphone jack. It also supports +48V phantom power if you need to connect a condenser microphone.

In addition it appears to be well-tested on Linux, with several user reporting that the device just works.

## Popping trouble

However, the device seemed to have some trouble with PulseAudio, which is the default audio library used in Ubuntu. Everything works, meaning that any audio application was able to output sound, and recording in Audacity gave good sound quality, but whenever I started playback or recording after switching between applications, the sound card would hang for 2 seconds and make 4 popping sounds before returning to normal operation.

## The solution: JACK + PulseAudio JACK Sink

If you are going to do any serious recording in Ubuntu, or Linux in general, you should get to know JACK. It is an awesome audio library for Ubuntu that aims to make life easy for musicians, audio engineers or the occasional amateur that wants to do recordings. It runs on top of ALSA, meaning it will support almost any sound card you can think of, but does so in a way that gives you extremely low latency and doesn’t mess with sound quality. The downside? JACK doesn’t allow PulseAudio to play side-by-side with it. And every Ubuntu application tries to play through PulseAudio by default.

The solution is to install the pulseaudio-module-jack package, which will allow applications to connect to JACK, even when they have no support for JACK:

sudo apt-get install pulseaudio-module-jack

In addition, you should install a nice GUI that will allow you to control JACK easily. This is named QjackCtl:

sudo apt-get install qjackctl

After installing, just run QjackCtl from the command line or the Dash and start + connect to the JACK server.

After this is done, you may check the Connect window to see if PulseAudio JACK Sink is also running, which it should do by default.

Then you may open Ubuntu’s Sound Settings and set PulseAudio JACK Sink to be your Output device. From now on, all applications should work even though JACK is running.

If you wish to, you may change QjackCtl’s settings to make JACK start whenever QjackCtl is started, and afterwards add QjackCtl to your Startup Applications in Ubuntu. This way JACK will start whenever you start your computer.

## No more popping

After installing PulseAudio JACK Sink and QjackCtl, I no longer experience any popping, and the FocusRite Scarlett 2i2 works flawlessly. The sound quality is great and the latency minimal, so I would definitely recommend this sound card to any Linux user wanting to do some recording at home or on the go.

Even though I wish it would work right out of the box, installing two packages to get everything perfect is that much work, and I assume that someone figures out a good solution to merge PulseAudio and JACK in a way similar to the one I use by default sometime in the future.

## Monitoring your unit tests without lifting a finger

I love unit testing. First of all, I think it is a good idea to test separate units of the code, but after doing so for some time, I’ve come to realize that unit tests are great for managing the software development cycle too. It all boils down to the idea that you should write tests before you write your code.

Now, this is something that I and others apparently struggle a lot with. How do you write a test for some code that doesn’t even exist yet? Even worse, how do you write a test for a piece of software that you’re not yet sure how will be used?

In computational physics, this problem arises often because we are writing code at the same time as we are trying to understand the physics, mathematics and algorithms at hand. And this is a good thing. You might want to think that one should structure all code before it is written, but this is generally a bad approach in computational physics. Especially if you’re working on something new. The reason is that you will often understand the problem and algorithms better while developing, rather than just reading about them and trying to analyze them blindly.

## Keeping the tests and code healthy

But enough with the talk, let’s just assume that you are convinced that you should (or have to) implement some unit tests. At one point you are likely to be in a position where you find it tiresome to have to go into that folder where the tests are defined and run them manually. This is where Jenkins comes in to play.

## Setting up UnitTest++ with Qt Creator in a nice project structure

Note: I’ve found a better way to visually verify that all tests are running. Check out this post on Jenkins to see how I’m now working with my tests. The below post is still useful as a reference on how to set up UnitTest++ in Qt Creator, also when using Jenkins.

Note 2: A new and, in my opinion, better project structure is shown in this new post.

Note 3: See this post for the same project structure using the even better Catch testing framework.

When you want to make sure that your code is working properly, it is a good idea to divide it into smaller, independent pieces that may be tested individually. A unit test is a short  code that tests a smallest possible portion of your application. It is a good idea to write tests as you go and it can even be useful to write a test before you even implement the function that will be tested.

With the combination of UnitTest++ and Qt Creator, I’m now able to write unit tests while working on the code and also have some nice visual indication about failed tests during the build step of my project:

During my search for a good setup for testing my applications I realized there were a few needs that I wanted to satisfy:

1. Creating new unit tests should be dead-easy to do. I want to spend as little time as possible on reading documentation about the testing framework.
2. Tests should be run immediately after a new build of the source code, automatically and without the extra hassle to remember to run the tests.
3. Tests should provide visual feedback with an easy way to get to where the tests fail. This should show up in the IDE or some other useful GUI tool.
4. The testing framework should be fairly easy to install, especially on Ubuntu. This is because I want to be able to promote it to my fellow students.

Ovito is a great tool to visualize atoms from molecular dynamics simulations and to perform some statistical analysis on the data. The tool is an alternative to other similar tools such as VMD and ParaView.

The current version of Ovito in the Ubuntu repositories (version 0.9.2) is sadly very outdated. Even though you of course may download the latest version from Ovito’s webpages and install it locally in your home folder, I often find it better to get a newer package version.

At the Computational Physics group’s PPA I have now uploaded the latest build of Ovito for Ubuntu in a package that will automatically replace the current Ovito version. Note that this is not a release version of Ovito, but the latest version fetched from Ovito’s sources (currently nicknamed 1.1.1.90). The reason is that Ovito’s creator, Alexander Stukowski, was kind enough to implement a suggestion we proposed to change the default input handler for the viewports to be the orbit input handler. This behavior feels so much more natural and makes the already great Ovito application even better.

To install the latest version of Ovito, all you need to do is to open up a terminal and type these lines:

sudo apt-add-repository ppa:comp-phys/stable
sudo apt-get install ovito

Note that the Computational Physics repository also contains newer versions of the Armadillo package, which will automatically be updated if you do not remove the repository after installing Ovito.

## Installing the nVidia driver in Kubuntu 12.04

Running the vanilla install of Kubuntu 12.04 worked incredibly well. It took me quite some time to notice that I was in fact using the open source noveau driver. Dual displays, desktop effects and all other first impressions worked without glitches. In fact, it was not before I tried to run Google Maps’ WebGL version that I started noticing some rendering errors. And according to the noveau project’s own webpages, the OpenGL acceleration is exactly where noveau is still lacking.

In addition, the graphics card seemed to heat itself more easily with the noveau driver.

Sadly this lead me to realize that I would still have to use the proprietary NVIDIA driver to make use of my graphics card and the applications I use daily. Even worse, getting this installed would prove to harder than in earlier versions of Ubuntu. I don’t know if this is due to using Kubuntu or not, but if you should experience some of the same symptoms, here is how I fixed it.

First of all, the symptoms were as follows after installing the nvidia-current package:

• The computer started only with one display and with a very low resolution (640 x 480)
• Enabling the nvidia driver using jockey-kde or jockey-text resulted in errors such as
• ERROR: XorgDriverHandler.enable(): package or module not installed, aborting
• WARNING: modinfo for module nvidia_current_updates failed: ERROR: modinfo: could not find module nvidia_current_updates
• Finally, installing nvidia-current only gave the error:
• Module build for the currently running kernel was skipped since the
kernel source for this kernel does not seem to be installed.

So, if you experience any of these, the reason is most likely missing kernel source and header libraries. The fix is thankfully simple, just run the following commands in a terminal:

sudo apt-get update
sudo apt-get purge nvidia-current
sudo apt-get install linux-source
jockey-text -e xorg:nvidia_current
nvidia-settings