TheilD within group inequality

[RicoFio]

Hi there!

I am currently trying to use the TheilD index for my research on transport access equality. As far as I understood, the definition of the decompose Theil index is this one. Then, what also makes sense to me, both components are defined positively and, accordingly the Theil index is bound in [0,inf].

Hence this result seems weird to me:

from inequality.theil import TheilD
TheilD(np.array([0,0,0,10,10,10]),[0,0,0,1,1,1]).wg[0]
>>> -0.6931471805599453

This arises because the within-group inequality is calculated by doing self.wg = T - bg in theil.py L 129.
Probably, I misunderstood something -> clarification on how to interpret this within-group component would be highly appreciated.

Cheers!