As of July 10 2014 this repository is now depending on aurespf as a submodule rather than old snapshots of the solver.
The _less.py files are clones of the old files with similar names. The difference is updated (less) dependencies.
To run the flow tracing algorithm refer to the wrapper function calc_usage in usage_old.py.
For vector flow tracing look at vector.py. It contains an implementation that builds on top of the up/down stream flow tracing algorithm.