Table 6 Setting parameters of GEP model.

From: Enhancement of groundwater resources quality prediction by machine learning models on the basis of an improved DRASTIC method

GEP parameters

Values

Number of chromosomes

30

Linking function

 + 

Mutation

0.00138

Gene recombination

0.00277

Fixed-root mutation

0.0068

Fitness function

Mean Square error

Best fitness function

510.739

Number of generation

576

Maximum depth of tree

4

Number of genes

4

Termination condition of GEP development

R-squared

Mathematical operators

Exp,LN,X2,3RT,Atan,Min(x1,x2),

Max(x1,x2),Avg(x1,x2),Tanh,NOT,Inv, + ,-,*,/

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