The vars argument expects a list or vector with named elements.
Every element name corresponds to the widget name which will be updated
with the supplied element value.
The vector, matrix, and data widgets can be updated in
several ways. If more than one name is specified for the names argument
of these widgets, each element is treated like an entry widget.
If however, a single name describes any of these three widgets, the entire
widget can be updated by passing an appropriately sized object.
Alternatively, any element can be updated by appending its index in square brackets
to the end of the name. The data widget is indexed differently
than the matrix widget by adding "d" after the brackets. This tweak is necessary
for the internal coding (bookkeeping) of PBS Modelling. Example: "foo[1,1]d".