The directory containing the root of the VTR source tree.
For instance, if you extracted/cloned the VTR source into ``/home/myusername/vtr``, your ``$VTR_ROOT`` would be ``/home/myusername/vtr``.
Minimum Width Transitor Area (MWTA) is a simple process technology independent unit for measuring circuit area.
It corresponds to the size the smallest (minimum width) transistor area.
For example, a 1x (unit-sized) CMOS inverter consists of two minimum width transistors (a PMOS pull-up, and NMOS pull-down).
For more details see :cite:`betz_arch_cad` (the original presentation of the MWTA model), and :cite:`chiasson_coffe` (an updated MWTA model).