The directory containing the root of the VTR source tree.
For instance, if you extracted/cloned the VTR source into
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 [betz_arch_cad] (the original presentation of the MWTA model), and [chiasson_coffe] (an updated MWTA model).