Compute response value to raw prediction such as linear predictor in GLM
gfunc(mu, family, epsbino)
linear predictor f=x'b for predictor x and coefficient b if the model is linear
vector of numbers as response value in GLM, for instance, probability estimation if family=2
integer from 1-4, corresponding to "gaussian", "binomial", "poisson", "negbin", respectively
a small positive value for family=2
to avoid numeric unstability