Matlab is a high-level language, primarily intended for numerical computations. The package is commercially distributed by the Mathworks. If you don't have the resources to purchase Matlab, you can run use Octave, which offers similar functionality.
Matlab R2011, R2012, R2013, R2014 and R2015 have been tested with 20-sim scripting but older versions may also work fine.
See the Matlab documentation from the Mathworks for information on installing Matlab. No special (additional) installation is needed to use 20-sim scripting from Matlab.
Note: Scripting in Matlab is similar to Octave. You can type exactly the same commands as given for Octave in the next sections.