The major problem was that Matlab complained about that I have the wrong version of X11 installed on my system and it won't start. As I have finished teaching today for the semester, I thought that I am going to celebrate this by resolving this issue which I was struggling with for a year or so by now. On the internet you will see a lot of advice on what to do, and as they say, the truth is indeed out there, however, it is not so easy to find. In a nutshell what seems to happen is this:
Why Matlab does not start when other applications do start (say, Gimp, Gnuplot using X11, etc.).
Matlab seems to make the assumption that the X11 libraries are located at /usr/X11/lib and it sticks to this assumption no matter how your system is configured. I use XQuartz and macports' X11 and they put stuff elsewhere. I had some legacy code sitting in /usr/X11/, which I did not use. It was a remainder of some version of X11 that I used probably 2 or 3 laptops ago. Matlab reported that the lib was found, but the "architecture was wrong". The error message had something like:
.. Did find: /usr/X11R6/lib/libXext.6.dylib: mach-o, but wrong architecture..
Anyhow, here is one solution.
You have to arrange that /usr/X11 points to a directory that has a working X11 copy.
It is probably a good idea to first clean up the old X11 installation. You can do this by following the advice on the XQuartz FAQ page by issuing the following commands in the terminal:
sudo rm -rf /usr/X11* /System/Library/Launch*/org.x.* /Applications/Utilities/X11.app /etc/*paths.d/X11 sudo pkgutil --forget com.apple.pkg.X11DocumentationLeo sudo pkgutil --forget com.apple.pkg.X11User sudo pkgutil --forget com.apple.pkg.X11SDKLeo sudo pkgutil --forget org.x.X11.pkgThen I have reinstalled the latest XQuartz copy (not all these steps might be necessary, but in order to stay on the safe side, I will describe everything I did).
I also have macports and xorg-libX11, xorg-libXp, xorg-server seems necessary for the following steps to succeed (but possibly other xorg-* ports are also needed). I am guessing that XQuartz does not install all the libraries, but after installing enough xorg-* ports through macports, all the libraries will be installed which are used by Matlab.
Now, my X11 is located at /opt/X11 and some additional libs are found at /opt/local/lib.
So I created a bunch of symbolic links:
sudo ln -s /opt/X11 /usr/X11
for i in /opt/local/lib/libX* ; do sudo ln -s $i /usr/X11/lib; done
The first line creates a symbolic link to /opt/X11, while the second is necessary because of the additional libX* libraries which, for some reason, macports puts into /opt/local/lib instead of puttting it into /opt/X11/lib. Initially I did not know that I need these libs, and then Matlab complained that it did not find the image for some lib (it was /usr/X11/lib/libXp.6.dylib).
Anyhow, I am really happy that this worked!
I hope people who will have the same trouble will find my post useful.