In the AaD loss objective Li(Ci,Bi)=−∑j∈CipiTpj+λ∑m∈BipiTpm, the dispersing term prevents feature representation collapse early in training. As adaptation proceeds and semantic clusters form, samples belonging to the same class appear in the mini-batch background set Bi, making a strong dispersing penalty detrimental. To mitigate this class-collision effect, the weighting parameter λ is decayed over iterations:
λ=(1+10⋅max_iteriter)−β
where iter is the current iteration step, max_iter is the maximum number of iterations, and β≥0 is the decay exponent.
The decay parameter β is chosen completely unsupervisedly using Soft Neighborhood Density (SND). Higher SND values correlate with superior target adaptation quality. Unsupervised grid search over β∈{0,0.25,0.5,1,2,3,4,5,7} via SND selects β=0 for Office-Home, β=2 for Office-31, and β=5 for VisDA-C.