Soft models and synthesis

In Chapter 2 it was stated that it is reasonable to assume that there is some functional relation between the experimental variables, Xj, X2..Xt and the observed response, y. 

As was seen in the preceeding section on hard models it is evident that it will be very difficult to derive an analytical expression for the function/by theoretical means. For practical purposes, it is, however, possible to use experiments to establish sufficiently good local approximations of the function/. 

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