WebSocket Test

# Installing qutip on Windows

I had some problems installing Qutip on Windows.
I solved them by adding the MinGW32-xy path to the Windows path environment.
See details here.

# Getting started with Python

I’ve written a short introduction to getting started with Python including IPython and how to set a default search path.
It is mostly targeted Ubuntu users.

# Ubuntu 14.04: Making it useful

sudo apt-get update && sudo apt-get dist-upgrade -y && sudo apt-get autoremove

sudo apt-get install ipython-notebook htop vim flashplugin-installer nautilus-open-terminal spyder tortoisehg-nautilus network-manager-openconnect ssh

# Total differentials

Total differentials are useful but how do you technically go from them to differentials of functions. Let’s define $f(x)$ as a continuous function.

Then

$$df= \frac{\partial f}{\partial x} dx,$$

where df is called the total differential. If x(t) is a function t then how do we get this explicit dependence?

$$f = \int df = \int \frac{\partial f}{\partial x} dx,$$

where we have used the fundamental theorem of calculus. Now we can perform a change of variables using the total differential of x ie. $dx=dx/dt dt$:

$$f = \int \frac{\partial f}{\partial x} dx = \int \frac{\partial f}{\partial x} \frac{dx}{dt} dt,$$

which can be differentiated with respect to time to give

$$\frac{df}{dt} =\frac{\partial f}{\partial x} \frac{dx}{dt}.$$

Here we changed the variables of the integrals (so be careful of the integral limits)

# Getting the newest version of Octave for Ubuntu/Debian

If you want the newest version of Octave (3.8 as of the time of writing) you will need to compile it yourself.

Do

sudo apt-get build-dep octave
sudo apt-get install libqscintilla2-9 libqscintilla2-dev
wget ftp://ftp.gnu.org/gnu/octave/octave-3.8.0.tar.bz2
tar -xvf octave-3.8.0.tar.bz2
cd octave-3.8.0
./configure
make
make check
sudo make install

when this is done Octave should work for you. Keep an eye out for warnings though. This was tested on Ubuntu 13.04 64 bit. If you use Debian you will need libqscintilla2-8 instead of 9. I  am actually not sure if you only need the dev package. On Debian you will also need to install libxft2-dev since this is not installed by default.

To run Octave with the GUI enabled run

octave –force-gui

this enables the GUI. The GUI is still in beta though so it might be a bit rough.

# Fase-skift i øvelse 5

Det kan være svært at fitte til arctan i forbindelse med målingen af fasen i øvelse 5 i Mekanik og Termodynamik. Her er en lille forklaring og et udtryk med cosinus man kan bruge i stedet:

phase