Generally, the Software should run fine in plain MATLAB and Octave. However, for optimal performance of the projection based approaches it can be advantageous to have the corresponding control systems toolbox providing optimized solvers for dense Lyapunov and Riccati equations.
Simply unpack the content of the archive to some folder, change to that folder before you use it and run mess_path. This will add this folder together with all required subfolders to your MATLAB/Octave search path. If you do not want to do this every time you need to work with M.E.S.S., simply run mypath = mess_path; and add the content of mypath to the default search path permanently.
If you have used an earlier version of M-M.E.S.S, make sure to remove it completely (especially from the MATLAB path in case you added it permanently).
Running multiple version in parallel with temporary path additions is not a problem.
This is the MATLAB toolbox file based download. Simply open the downloaded file in the MATLAB directory browser and it should automatically install the toolbox and set the paths correctly.
If you have an earlier version of the toolbox installed already we recommend removing it first.
This is the Octave package file intended for use with the Octave package manager pkg. On the Octave prompt, change to the folder where the download is located and run pkg install mess-2.2.tar.gz.
Since this package depends on the control package for the solution of small dense Lyapunov and Riccati equations, make sure to have that package installed already. This can be done, e.g. by running pkg install -forge control with an active internet connection, to fetch and install the package from Octave-Forge directly.