Data are sampled from the modified math function based on the first example in the paper listed in codereferences.
There are still 2 quantitative and 1 qualitative variables, but the qualitative variable has only 3 levels.
For each level, there are 8 training data points and 30 testing data points, all generated with Latin hypercube sampling.
In total, there are 24 training data points and 90 testing data points.