There are several variants of GCCA (Kettenring, 1971); we follow Bach and Jordan (2002) and solve a multiview version of Equation 1: For stability, we add τ σ j I j to every covariance matrix Σ j,j , where τ is a hyperparameter (here: τ = 0.1), I j is the identity matrix and σ j is the average variance of x j .
1 To overcome this problem, two avenues have been explored: The first is supervised domainadversarial training on a label-rich source forum (Shah et al., 2018), which works best when 10 0 10 1 10 2 10 3 10 4 10 5 10 6 #D #Q source and target domains are related.