some questions about result of D-statistics(qpDstat)

[Zhuoran Kuang]

Hi !!!
from README.Dstatistics,I read these:

D = num/ den
well, It's not the same as "ABBA-BABA" that I often see

and
If the Z-score is +ve, then the gene flow occured either between W and Y or X and Z
If the Z-score is -ve, then the gene flow occured either between W and Z or X and Y.

what does "+ve" or "-ve" mean? Do these mean >0 or <0 ?

And How do I determine between which two groups the gene flow occurs.
I learned that W, X, Y, Z to satisfy such a relationship: (((W, X), Y), Z), to determine, when D / Z-score greater than 0, and gene flow occurred in the W Between Y, less than 0 occurs between X and Y.

Or I can set Z to be an obvious outgroup, then the phylogenetic relationship above does not need to be satisfied, and I can also determine whether the gene flow occurs between W and Y (D>0) or between X and Y (D <0)

At last，It's about visualization. A fixed WXYZ combination has only one value(D/Z-score), so it cannot draw the D statistical results shown in box plots that I often see.

[Shangzhe Zhang]

I have no idea either!