Table 5.

Configuration settings for GEP algorithm.

	Parameter	Ω2	Ω4	Ω6
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