1. add a new function called entropic\_partial\_wasserstein\_logscale to

ot.partial. This function solves the same problem as
entropic\_partial\_wasserstein but is computed in logscale, so it is
more robust.

2. Test exampless are provided in compare_logscale_POT.py. Test data is
   in data\entropic_partial_OT_cost.txt

Author: wzm2256