I think I am asking a more general question, using specifics as examples.  For instance, If I sampled flours – wheat, rye, millet, buckwheat,…. and created a good categorical model that could identify each.  If I then mixed two different flours together, how can I create a model that will say ” 50% rye, 50% millet”?  I think right now the models just try to find the best categorical fit and does not try to match linear combinations of categories, right?