Define a criterion to optimize

To analyze the results it is necessary to have a criterion of optimality. Often, the most interesting response, e.g. the yield of the desired product, is used as the criterion. The objective is the to maximize the response, or to reach a level which is satisfactory. 

The method of steepest ascent and the simplex search can handle only one criterion, while the resportse surface methods allow simultaneous mapping of several responses. Response surface modelling can therefore be used to optimize several responses simultaneously. The problem of multiple responses is elegantly handled by PLS modelling. This technique is discussed in Chapter 17. 

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