When the water mass fraction of the substrate is about 45%, its EC can be predicted accurately by both the power function as well as the linear function models.

In designing methods of fitness function there are many ways, for examples: linear transformation, power transformation, index transformation, variance adjustment, etc.

For optimal model - reduction of large scale systems, up to now, the integral-square - error method has been developed for systems with impulse, power or sine function inputs only.