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sra2's Introduction

SRA2: Stochastic ranking-based multi-indicator algorithm with archive

Reference: B. Li, K. Tang, J. Li, and X. Yao, Stochastic ranking algorithm for many-objective optimization based on multiple indicators, IEEE Transactions on Evolutionary Computation, 2016, 20(6): 924-938.
SRA2 is a many-objective evolutionary algorithm (MaOEA) which implements multiple indicators and stochastic ranking in environmental selection. This program implements SDE (shift-based density estimation) and $I_{\epsilon+}$. SRA2 is an improved version of SRA with an external archive.
Variables Meaning
npop Population size
iter Iteration number
lb Lower bound
ub Upper bound
T Neighborhood size (default = 20)
nobj The dimension of objective space (default = 3)
eta_c Spread factor distribution index (default = 15)
eta_m Perturbance factor distribution index (default = 15)
pt_min The minimum probability parameter (default = 0.4)
pt_max The maximum probability parameter (default = 0.6)
nvar The dimension of decision space
pop Population
objs The objectives of population
arch Archive
arch_objs The objectives of archive
V Reference vectors
B The T closet weight vectors
zmin Ideal point
mating_pool Mating pool
off Offspring
off_objs The objective of offsprings
dom Domination matrix
I1 $I_{\epsilon+}$ indicator
I2 SDE indicator

Test problem: DTLZ1

$$ \begin{aligned} & k = nvar - nobj + 1, \text{ the last $k$ variables is represented as $x_M$} \\ & g(x_M) = 100 \left[|x_M| + \sum_{x_i \in x_M}(x_i - 0.5)^2 - \cos(20\pi(x_i - 0.5)) \right] \\ & \min \\ & f_1(x) = \frac{1}{2}x_1x_2 \cdots x_{M - 1}(1 + g(x_M)) \\ & f_2(x) = \frac{1}{2}x_1x_2 \cdots (1 - x_{M - 1})(1 + g(x_M)) \\ & \vdots \\ & f_{M - 1}(x) = \frac{1}{2}x_1(1 - x_2)(1 + g(x_M)) \\ & f_M(x) = \frac{1}{2}(1 - x_1)(1 + g(x_M)) \\ & \text{subject to} \\ & x_i \in [0, 1], \quad \forall i = 1, \cdots, n \end{aligned} $$

Example

if __name__ == '__main__':
    main(100, 300, np.array([0] * 7), np.array([1] * 7))
Output:

The upper figure is the Pareto front obtained by the SRA, and the lower one is the SRA2. It can be seen that SRA2 can obtain more evenly distributed Pareto optimal solutions.

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