Pairwise constraints

[zdk123]

I love the method and fantastic code base.

I'm wondering if you've thought about an extension for pairwise constraints rather than regression. For instance in alignf, the kernel alignment depends on the matrix Ky = y*y', where y is the predictor variable. Ky could rather be a matrix with entries k_ij, encoding side information about the relationship between sample i and j instead.

Also similar in setup to this method

thanks!