Table 5 Configuration settings for GEP algorithm.

General

No. of chromosomes

40

40

30

head size

18

15

10

No. of genes

6

8

12

linking function

Addition

Addition

Addition

function set

 + , −, *, /, Exp, Ln, Inv, x², 3Rt, Min 2, Ave 2, Max 2, Atan, Tanh, NOT

 + , −, *, /, Pow, Sqrt, Exp, Pow10, Ln, Log, Inv, x², x³, x⁴, x⁵, 3Rt, 4Rt, 5Rt, Min 2, Ave 2, Max 2, Atan, Tanh, NOT

 + , −, *, /, Pow, Sqrt, Exp, Pow10, Ln, Log, Abs, Inv, x², x³, x⁴, 3Rt, 4Rt, Min 2, Max, 2Ave 2, Ave 3

Fitness function

RMSE

RMSE

RMSE

Genetic operators

Mutation rate

0.00138

0.00138

0.00138

IS transposition rate

0.00546

0.00546

0.00546

RIS transposition rate

0.00546

0.00546

0.00546

Inversion rate

0.00546

0.00546

0.00546

Gene recombination

0.00277

0.00277

0.00277

Gene transposition

0.00277

0.00277

0.00277

Numerical constants

Constants per gene

10

10

10

Data type

Floating-point

Floating-point

Floating-point

Lower bound

− 10

−10

−10

Upper bound

 + 10

 + 10

 + 10