relax SVN archive

Improvement in the comments from the gnuplot correlation_matrix() plotting API function.

Significantly expanded the gnuplot script from via the correlation_matrix() plotting API function.

This is for the structure.atomic_fluctuations user function. The output terminal is now set to EPS,
the colour map changed from the default to a blue-red map, labels have been added, the plot is now
square, and comments are now included throughout the script to help a user hand modify it after
creation.

The gnuplot correlation_matrix() plotting API function now creates a text file of the data.

The lib.plotting.gnuplot.correlation_matrix() function now calls the
lib.plotting.text.correlation_matrix() function prior to creating the gnuplot script.

Fix for the structure.atomic_fluctuations user function backend.

The pipe_control.structure.main.atomic_fluctuations() function no longer opens the output file.

More simplifications for the structure.atomic_fluctuations user function backend.

Shifted the matrix output of the structure.atomic_fluctuations user function into lib.plotting.text.

The new lib.plotting.text module will be used by the relax library plotting API to output data into
plain text format. The current correlation_matrix() function, which has been added to the API
correlation_matrix() function dictionary, simply has the file writing code of the
structure.atomic_fluctuations user function. This significantly simplifies the user function.

Enabled the gnuplot format for the structure.atomic_fluctuations user function.

This uses the plotting API correlation_matrix() function for visualisation. The change allows the
Structure.test_atomic_fluctuations_gnuplot system test to pass.

Implemented a very basic gnuplot backend for the correlation_matrix() plotting API function.

This is in the new lib.plotting.gnuplot module. It creates an incredibly basic gnuplot script for
visualising the correlation matrix, assuming a text file has already been created.

Created the lib.plotting API function correlation_matrix().

This is the lib.plotting.api.correlation_matrix() function. It will be used for the visualisation
of rank-2 correlation matrices. The current basic API design here uses a dictionary of backend
functions (currently empty) for calling the backend.

Created the Structure.test_atomic_fluctuations_gnuplot system test.

This checks the operation of the structure.atomic_fluctuations user function when the output format
is set to 'gnuplot'. This will be used to implement this option. The current gnuplot script
expected by this test is just a very basic starting script for now.