The error was found by:
relax_trunk --time -s Relax_disp.test_repeat_cpmg -d
And the error generated was:
QXcbConnection: Could not connect to display
Aborted (core dumped)
The backend of matplotlib have to be changed.
This is for example described in:
http://stackoverflow.com/questions/2766149/possible-to-use-pyplot-without-display
http://stackoverflow.com/questions/8257385/automatic-detection-of-display-availability-with-matplotlib
The solution is:
import matplotlib
if not "DISPLAY" in environ:
# Force matplotlib to not use any Xwindows backend.
matplotlib.use('Agg')
