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This article was downloaded by: [National University of Sciences & Technology]On: 30 October 2014, At: 23:22Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
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A discrete artificial bee colony
algorithm incorporating differential
evolution for the flow-shop scheduling
problem with blockingYu-Yan Hana, Dunwei Gonga & Xiaoyan Suna
a School of Information and Electrical Engineering, China
University of Mining and Technology, Xuzhou, PR China
Published online: 18 Jun 2014.
To cite this article: Yu-Yan Han, Dunwei Gong & Xiaoyan Sun (2014): A discrete artificial bee colonyalgorithm incorporating differential evolution for the flow-shop scheduling problem with blocking,
To link to this article: http://dx.doi.org/10.1080/0305215X.2014.928817
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
A discrete artificial bee colony algorithm incorporating
differential evolution for the flow-shop scheduling problem
with blocking
Yu-Yan Han, Dunwei Gong∗ and Xiaoyan Sun
School of Information and Electrical Engineering, China University of Mining and Technology,
Xuzhou, PR China
( Received 26 December 2013; accepted 19 May 2014)
A flow-shop scheduling problem with blocking has important applications in a variety of industrial systemsbut is underrepresented in the research literature. In this study, a novel discrete artificial bee colony (ABC)algorithm is presented to solve the above scheduling problem with a makespan criterion by incorporatingtheABC with differential evolution (DE). The proposed algorithm (DE-ABC) contains three key operators.One is related to the employed bee operator (i.e. adopting mutation and crossover operators of discrete DEto generate solutions with good quality); the second is concerned with the onlooker bee operator, whichmodifies the selected solutions using insert or swap operators based on the self-adaptive strategy; and thelast is for the local search, that is, the insert-neighbourhood-based local search with a small probability is
adopted to improve the algorithm’s capability in exploitation. The performance of the proposed DE-ABCalgorithm is empirically evaluated by applying it to well-known benchmark problems. The experimentalresults show thatthe proposedalgorithmis superiorto the comparedalgorithmsin minimizingthe makespancriterion.
Flow-shop scheduling problems can be generally classified into the following two categories
according to whether there are buffers or not: one with infinite buffers, and the other with finitebuffers. The former does not result in blocking any job since there are enough intermediate
buffers to store those completed jobs. The latter only maintains a limited capacity of in-process
inventories, which means that there are either no buffers or buffers with a limited capacity owing
to the finite storage facilities. The flow-shop scheduling problem with no intermediate buffers
considered here, named the blocking flow-shop (BFS) scheduling problem, is a special case of
the latter. For this case, a job must remain in the current machine until the next machine is available
for processing, which increases the waiting time or the productive cycle, and thus decreases the
production efficiency.
Owing to the above process characteristics, the BFS scheduling problem has been a typical
problem with a strong engineering background. In the chemical industry, partially processed jobs(i.e. physical or chemical materials) are held in machines because there is no intermediate storage
(Suhami and Mah 1981). For various processes in a manufacturing enterprise (Grabowski and
Pempera 2000), the intermediate product cannot be stored in some stages. In the case of the iron
and steel industry (Gong, Tang, and Duin 2010), the blocking of ingots in the soaking pit will result
in extra energy consumption since the blocked ingot requires a high temperature. With respect to
the computational complexity, it has been proved that the BFS scheduling problem with more than
two machines is NP hard (Storn and Price 1997, Allahverdi, Ng, and Cheng 2008). Therefore, it
is of great importance to seek appropriate methods to tackle the BFS problem.
With regard to the algorithms for solving the BFS scheduling problem with a makespan cri-
terion, the existing studies can be broadly classified into constructive heuristics and improved
metaheuristics. The former type uses specific rules to assign each job with a priority index to con-
struct a sequence, such as Nawaz–Enscore–Ham (NEH), profile fitting (PF) and MinMax (MM).
Nawaz, Enscore, and Ham (1983) first designed an NEH heuristic for the traditional flow-shop
problem with a makespan criterion, and the experimental results demonstrated the effectiveness
and efficiency of the proposed heuristic in comparison with existing algorithms. Since then, the
NEH heuristic has gained much attention and has been successfully applied to the BFS schedul-ing problem (Ribas, Companys, and Tort-Martorell 2011). McCormich et al. (1989) developed
a constructive heuristic, known as PF, for solving permutation problems in an assembly line.
In this heuristic, PF tries to generate a partial sequence by adding an unscheduled job so as to
minimize the sum of idle and blocking time on machines. Ronconi (2004) presented the MM
heuristic based on the makespan properties. In addition, they proposed two composite construc-
tive heuristics, called MME (the combination of MM and NEH) and PFE (the combination of PF
and NEH). Their empirical results showed that MME and PFE heuristics are superior to the NEH
heuristic. Recently, Pan and Wang (2012) designed two simple constructive heuristics for the BFS
scheduling problem, called the weighted profile fitting (wPF) and Pan–Wang (PW) heuristics,
based on the PF approach. They also developed three improved constructive heuristics, namely,PF-NEH, wPF-NEH and PW-NEH, by combining the procedure of the NEH heuristic with the
PF, wPF and PW, respectively. A series of BFS scheduling problem instances demonstrated that
the presented constructive heuristics perform significantly better than the existing ones.
The above constructive heuristics can rapidly yield feasible solutions. However, the quality
of these solutions is somewhat worse than that obtained by the metaheuristic algorithms (Li,
Wang, and Wu 2009). Caraffa et al. (2001) proposed a genetic algorithm (GA) to minimize the
makespan criterion for the BFS scheduling problem. In this work, each job sequence of the prob-
lem is viewed as a chromosome. Grabowski and Pempera (2007) presented tabu search algorithms
with and without multimoves (TS and TS + M, respectively) for the flow-shop scheduling prob-
lem with blocking, where a dynamic tabu list is used to overcome the local optima. Qian et al.
(2009) developed an effective hybrid differential evolution (HDE) to solve the flow-shop schedul-
ing problem with limited buffers between consecutive machines. Thereafter, Wang et al. (2010)
designed a novel hybrid discrete differential evolution (HDDE) to optimize the makespan criterion
for the BFS scheduling problem. To avoid the regions with local optima, Davendra et al. (2012)
adopted an enhanced differential evolution (EDEc) to solve the flow-shop scheduling problem
with blocking based on the segregation bias rules. The proposed EDEc algorithm obtained 49 new
upper bounds for the Taillard problems. Since then, DE has been successfully applied to different
problems owing to its powerful performance (Ramesh, Kannan, and Baskar 2012; Zhu, Yan, and
Zhao 2013). In addition, for the same problem, Wang and Tang (2012) presented a discrete particle
swarm optimization (DPSO) to minimize the makespan objective of the BFS scheduling problem
with m machines. In this work, they adopted a self-adaptive strategy to control the diversity of population. In addition, they provided a stochastic variable neighbourhood search approach to
improve the exploration.
The artificial bee colony (ABC) algorithm, one of the most recent swarm intelligence
approaches, was presented by Karaboga (2005). As the name implies, this algorithm simulates
the foraging behaviour of honey bee colonies. ABC was commonly used for optimization prob-
lems with continuous variables, and showed promise in terms of accuracy and efficiency (Kang,
Li, and Ma 2013). However, owing to the continuous nature of the basic ABC algorithm, it
cannot be directly used to generate a feasible job permutation for the flow-shop scheduling
problem. To overcome such a drawback, Pan et al. (2011) first proposed a discrete artificial
bee colony (DABC) algorithm for the lot-streaming flow-shop scheduling problem. There-
after, Han, Duan, and Zhang (2012) applied an improved DABC algorithm to tackle the BFS
scheduling problem, and the experimental results demonstrated that the proposed algorithm
outperforms the HDDE, DABC, GA, TS and TS + M algorithms in minimizing the makespan
criterion.
Among the aforementioned metaheuristic algorithms, the DDE and DABC algorithms are the
most powerful and have been successfully applied to the BFS scheduling problem. However, both
the employed and onlooker bees in the existing DABC algorithms adopted the insert or swap
operator to produce new neighbouring solutions, which may be local optima. Besides, the DABC
algorithm spends a lot of computation time on repeated search, which greatly reduces the con-vergence speed and the efficiency of the algorithm. To tackle these problems, a hybrid algorithm,
integrating DDE and DABC algorithms, was proposed. In the literature, hybrid algorithms often
obtain results of high quality. Fan, Liang, and Zahara (2004) employed a hybrid simplex search and
particle swarm optimization (PSO) to solve multimodal optimization problems. Xu et al. (2014)
embedded a local search into the artificial immune algorithm for solving a distributed permutation
flow-shop scheduling problem. Huang and Shiau (2008) presented a hybrid algorithm based on the
column generation and the constructive heuristic for a proportionate flexible flow-shop scheduling
problem. Following that, for the same problem, Shiau and Huang (2012) proposed a hybrid two-
phase encoding particle swarm optimization (TPEPSO) algorithm and the experimental results
demonstrated its robustness. Han et al. (2014) embedded the estimation of distribution algorithm(EDA) into NSGA-II to replace traditional crossover and mutation operators and the experimental
results demonstrated the superiority of the hybrid algorithm in terms of quality. In this study, the
proposed hybrid algorithm, DE-ABC, was also empirically demonstrated to perform better in
exploration and exploitation. According to the notation introduced by Graham et al. (1979), the
BFS scheduling problem with makespan criterion under study is denoted as Fm|blocking|C max
throughout this article.
To sum up, in this study, the proposed algorithm makes three main contributions: (1) the
mutation and crossover operators are adopted to generate good solutions, instead of the insert
or swap operator in the employed bee stage; (2) the insert or swap operator based on the self-
adaptive strategy is employed to modify the given solutions in the onlooker bee stage; and (3) the
insert-neighbourhood-based local search with a small probability is performed so as to improve
the algorithm’s capability in exploitation.
The remainder of this article is organized as follows. In Section 2, the description of
Fm|blocking|C max is given. Section 3 addresses the basic ABC algorithm. The proposed algorithm
is presented in detail in Section 4. Section 5 provides the experimental results. Finally, the article
ends with some conclusions in Section 6.
2. Formulation of the blocking flow-shop scheduling problem
Table 1 lists the symbols and notations that will be used throughout this article.
The BFS scheduling problem with no buffers is formulated as follows. There are n jobs and m
machines. Each job from sequence π has to be processed on m machines without intermediate
buffers in the same series. Jobπ( j) has a sequence of m operations O j,k . Operation O j,k corresponds
Step 2: Randomly generate a solution in the search space. If it is distinct from all the existing
solutions in the population, then put it into the population; otherwise, discard it.
Step 3: Repeat Step 2 until the population has PS individuals.
4.2. Exploring new and unknown areas using the discrete differential evolution approach
The insert and swap operators, through which the neighbouring solutions are generated, show the
superiority of the DABC algorithm. However, in the existing DABC algorithm, both the employed
and onlooker bees adopt the insert or swap operator to yield new solutions. Because of such a
repeated search, the neighbouring solutions obtained by them may be local optima. Thus, the
previous DABC algorithm finds it difficult to explore the entire solution space, which indicates
that it is weak in exploration. The merit of DDE is that it takes advantage of the differences among
individuals in the population to seek the global optimal solution. That is, DDE has the capability
to escape from the local optima. Therefore, the DDE algorithm is incorporated into DABC to
yield new solutions instead of the insert or swap operator in the employed bee stage. Since DDE
contains two critical operators, i.e. the mutation and crossover operators, an individual or jobpermutation π is first generated by performing the mutation operator. The job permutation, π ,
itself may not include all jobs since some jobs may exist repeatedly, whereas others may be lost.
Therefore, the crossover operator is applied to generate a complete sequence of jobs. Figure 3
gives the pseudo-code of the mutation and crossover operators.
To simply illustrate the aforementioned steps, suppose that there are five jobs, and the values
of the parameters pmu and pc are equal to 0.9 and 0.1, respectively. Let πref = {1,2,3,4,5}. An
example of constructing a new solution using the mutation and crossover operators is shown in
the following.
(1) Randomly select three solutions, πa = {2,1,4,3,5}, πb = {4,2,5,1,3} and πc =
Figure 4. Pseudo-code of the self-adaptive strategy.
4.3. Modifying the selected solutions using a self-adaptive strategy
The onlooker bees use the tournament selection to share some solutions generated by the employed
bees, and adopt the insert or swap operator to modify them based on a self-adaptive strategy so as to
search for outstanding neighbouring solutions. The insert operator randomly selects two positions, p1 and p2 ( p1 < p2), from a sequence π and moves all jobs between the positions p1 + 1 and p2
forward a position in turn, whereas the swap operator just interchanges the corresponding jobs
between positions p1 and p2 ( p1 < p2). Figure 4 describes the pseudo-code of the self-adaptive
strategy based on the insert and swap operators.
4.4. Updating unchanged solutions
As addressed in the basic ABC algorithm, after the employed bees and onlooker bees have finished
their search, the algorithm checks whether or not there are any exhausted or unchanged solutions.
Next, these unchanged solutions are replaced with the new ones discovered by the scout bees.The scout bees play a role in realizing the negative feedback mechanism and the fluctuation
property in the self-organization of the ABC algorithm (Akay and Karaboga 2012). In the basic
ABC algorithm, the scout bees randomly generate solutions to replace those unchanged ones.
This process enhances the diversity of the population, but it also reduces the search efficiency.
Therefore, each scout bee performs several insert operators on the unchanged solutions in this
study.
4.5. Local search
As a simple neighbourhood search approach, the local search seeks a better solution in the neigh-bourhood of a given solution. It has been shown that the insert-neighbourhood-based local search
(Ruben and Stutzle 2008) is superior to TS and the simulated annealing (SA) algorithm (Ruben and
Concepcion 2005). Therefore, this local search is adopted to enhance the ability of the proposed
algorithm in exploitation. In this study, the local search is performed on the solutions selected by
the onlooker bees stage with a small probability of pls, which controls whether or not a solutionperforms the local search. Specifically, a random value, r , is generated in the range of [0,1]. If r
is less than pls, then the solution performs the local search. Figure 5 states the pseudo-code of the
local search.
4.6. Summary of the proposed algorithm
In summary, the steps of the proposed algorithm are as follows:
Step 1: Set the values of the parameters used in the proposed algorithm and initialize the
population by using MME and the random method stated in Subsection 4.1.Step 2: Perform the mutation and crossover operators presented in Subsection 4.2 to produce
outstanding solutions.
Step 3: Modify the selected solutions using the self-adaptive strategy given in Subsection 4.3.
Step 4: Carry out the local search to seek a better solution from the neighbourhood of a given
solution with the probability of pls.
Step 5: Obtain new solutions by applying several insert operators to the unchanged solutions
in the whole population and replace the exhausted ones according to the approach described
in Subsection 4.4.
Step 6: Judge whether the termination criterion of the algorithm is met or not. If it is, stop the
evolution of the population and output the optimal solutions; otherwise, go to Step 2.
5. Experiments
In this section, the proposed algorithm is applied to some typical instances of the BFS scheduling
problem and compared with six existing available algorithms to evaluate the performance of the
proposed algorithm. The proposed algorithm is written with C++, and implemented on a personal
computer with Pentium® Dual 2.79 GHz and 1.96 GB of memory.
5.1. Experimental setting
There are 120 instances from the well-known benchmark set provided by Taillard (1993). These
instances have also been used by the existing algorithms by treating them as Fm|blocking|C max.
They are divided into 12 groups of different sizes, each consisting of 10 instances of the same
size. The values of parameters, the size of instances and the maximal computation time adopted
by the proposed algorithm are set as follows:
• The population size, PS , the mutation probability, pmu, the crossover probability, pc, and the
local search probability, pls, are set to 20, 0.9, 0.1 and 0.2, respectively.• The number of jobs for each instance is chosen from the set {20,50,100,200,500} and that of
machines is chosen from {5,10,20}.
• For each instance, the maximal computation time is set to 5 × m × n milliseconds.
The proposed DE-ABC algorithm is compared with the existing metaheuristics, i.e. TS + M
(Grabowski and Pempera 2007),HDDE (Wang et al. 2010), DABC (Han et al. 2011), IABC (Han,
Duan, and Zhang 2012), DPSOsvns (Wang and Tang 2012) and EDEc (Davendra et al. 2012). For
each instance, each method is independently run five times, the minimal makespan is recorded and
compared with the referenced makespan taken from the branch-and-bound method of Ronconi
(2005), and the average relative percentage difference of the five runs is obtained. For all instances
in a group, such average relative percentage differences are computed and denoted as the ARPD.The makespan of the jth instance provided by the ith algorithm in the t th run is denoted as
C i j,t , the referenced value of which, provided by Ronconi (2005), is C R j . In addition, the average
relative percentage difference obtained by the ith algorithm, denoted as ARPDi, can be expressed
as follows:
ARPDi =1
50
10
j=1
5
t =1
C R j − C i j,t
C R j× 100% (8)
It is clear that the larger the value of ARPDi, the better the result produced by the algorithm.
During the solving of the above instances, if a better solution of an instance is obtained using
the proposed algorithm than that of the comparative algorithms, its upper bound is updated. Thecomputational results related to the following aspects are reported in the experiments:
• comparison results between the proposed algorithm and the six comparative ones
• update of upper bounds of some benchmark problems
• convergence of different algorithms for six instances
• non-parametric test on ARPD indicator
• sensitivity analysis on parameters pmu, pc and pls used in the proposed algorithm.
5.2. Results and analysis
5.2.1. Comparison of DABC, IABC and DE-ABC
In this section, the proposed DE-ABC algorithm is compared with two existing ABC algorithms,
DABC and IABC. The essential difference between DABC and DE-ABC is that the former uses
the insert or swap operator in the employed bee stage, whereas the latter adopts the mutation
and crossover operators of DDE. In addition to the above difference, for the IABC and DE-
ABC algorithms, the other difference is that the latter employs only one of the four initialization
strategies provided by the former. Although the four initialization strategies of IABC have been
recognized as superior to the single one, DDE is beneficial in generating good solutions if the
proposed algorithm is better than IABC. Thus, this section provides the following experimental
results to demonstrate the performance of DDE in exploration.Table 2 reports the corresponding comparison results on the premise of the same computational
time and experimental environment. From Table 2: (1) for instances with a small scale, such as
20 × 5, 20 × 10 and 20 × 20, the proposed algorithm is slightly inferior to DABC and IABC
in the value of ARPD; (2) except for the above cases, the proposed algorithm is superior to
Note: Data in italic indicate the best value of ARPD for each group of instances among these algorithms.a Pentium Dual 2.79 GHz and 1.96 GB memory.
the comparative ones; and (3) on average, the ARPD value of DE-ABC is equal to 4.22, much
better than the values of 3.88 and 4.10 gained by DABC and IABC, respectively. The minimal
and maximal values of ARPD (MinAD and MaxAD, respectively) produced by DE-ABC are also
much larger than those generated by the DABC andIABC algorithms. Furthermore, the superiority
of the DE-ABC algorithm over the comparative ones increases along with the increment of the
problem size.
The following conclusion can be drawn from the above experimental results: the proposed
algorithm can take full advantage of the differentiation information among the population in theemployed bee stage to enhance the capability in exploration.
5.2.2. Comparison of EDEc, HDDE and DE-ABC
The HDDE and EDEc algorithms proposed by Wang et al. (2010) and Davendra et al. (2012),
respectively, can obtain better solutions than some existing algorithms, i.e. TS + M, GA and HDE,
suggesting that the algorithms based on DDE are more powerful. Although DDE has the capability
in exploration, it lacks the capability in exploitation. However, DABC can successfully search
for local optima in the neighbourhood of a solution, so the DE-ABC algorithm, by incorporating
DDE with DABC, can balance the capability in exploration and exploitation, which can be verifiedfrom Table 3.
As illustrated in Table 3: (1) for instances of 20 × 5, 20 × 10 and 20 × 20, the proposed
algorithm is slightly inferior to EDEc and HDDE; (2) except for the above cases and the 100 × 5
instance, the proposed algorithm outperforms the comparative ones; (3) the ARPD value, 4.22,
generated by DE-ABC is much larger than the values of 3.79 and 3.75 obtained by EDEc and
HDDE, respectively, indicating that the hybrid algorithm based on DDE and DABC does better
in exploration and exploitation than the above comparative ones.
From the above experimental results, it can be concluded that DE-ABC overcomes the shortage
of DDE in exploitation by incorporating DABC and obtains solutions with high quality.
5.2.3. Comparison of TS + M , DPSOsvns and DE-ABC
For blocking scheduling problems, there are two typical algorithms, i.e. TS + M and DPSOsvns.
The former is a benchmark and the latter has been recently developed. In this study, the proposed
Average 3.79 2.51 4.98 3.75 3.59 3.97 4.24 3.96 4.50
Note: Data in italic indicate the best value of ARPD for each group of instances among these algorithms.a Pentium Dual 2.79 GHz and 1.96 GB memory.bMacBook Pro, 2.4 GHz Intel Core 2 Duo, 2 GB RAM.
Table 4. Average relative percentage difference (ARPD) values of TS + Ma , DPSObsvns and DE-ABC.
TS + M DPSOsvns DE-ABC
n × m ARPD Time (s) ARPD Time (s) ARPD MinAD MaxAD Time (s)
Note: Data in italic indicate the best value of ARPD for each group of instances among these algorithms.a Pentium P-IV, 1000 MHz and 30,000 iterations.bIntel 2.33GHz CPU and 2 GB memory.
algorithm is compared with these, and associated comparison results are reported in Table 4. It
should be noted that the TS + M algorithm employed 30,000 iterations on an Intel 1 GHz CPU,
whereas both DPSOsvns and DE-ABC performed fewer than 2000 iterations on a Pentium 2.33
and 2.79 GHz CPU, respectively. Although the implementation environment in this study is better
than that of TS + M, fewer iterations are adopted here. Therefore, it can be seen that the value of
ARPD produced by DE-ABC is comparable with that of TS + M.From Table 4: (1) for all instances, DE-ABC clearly prevails over TS + M and DPSOsvns in the
value of ARPD; and (2) even the MinAD value of DE-ABC is much larger than that generated
by the TS + Mand DPSOsvns algorithms. These values demonstrate that the proposed algorithm
performs better in the value of ARPD than the comparative algorithms.
The excellent performance of the proposed algorithm encouraged the authors to seek new upper
bounds of Taillard’s benchmarks for the Fm|blocking|C max scheduling problem. Ronconi (2005)
first reported the upper bounds of 120 instances; following that, Grabowski and Pempera (2007)obtained 94 out of 120 upper bounds using the TS+M algorithm. Later, more algorithms, i.e.
HDDE, DABC, DPSOsvns, EDEc and IABC, provided newer upper bounds. Thus, in Tables 5 and
6, for each instance, the best solution yielded by the proposed algorithm is reported to update
some upper bounds.
As stated in Tables 5 and 6: (1) for the instances with a small scale, i.e. 20 × 5, 20 × 10 and
20 × 20, 30 best values of makespan obtained by DE-ABC are equal to the corresponding best
ones yielded by HDDE, DABC, DPSOsvns, EDEc and IABC, respectively; (2) for the remaining
90 instances, zero, six (6/90 = 7%), one (1/90 = 1%), zero, 11 (11/90 = 12%) and 10 (10/90 =
11%) new solutions produced by TS + M, DABC, HDDE, DPSOsvns, EDEc and IABC are found,
respectively, while 62 out of 90 (62/90 = 69%) new upper bounds provided by the proposedalgorithm are further improved. These experimental results clearly demonstrate that the proposed
algorithm can update more upper bounds of Taillard’s benchmarks than the comparative ones.
5.2.5. Convergence curves of different algorithms
To further evaluate the makespan values of different algorithms, in this section, the convergence
curves of the makespan values are investigated. For the Fm |blocking|C max scheduling problem,
Ta53, Ta72, Ta86, Ta96, Ta109 and Ta115 of Taillard’s benchmarks are selected, and their best val-
ues of makespan obtained by HDDE, DABC, DPSOsvns, EDEc, IABC andDE-ABC are calculated,
respectively, with the increment of computation time, shown as Figures 6–8.From Figures 6–8: (1) for each instance, each algorithm can obtain better and better makespan
values as the computation time increases; and (2) for the same computation time, the makespan
values of the proposed algorithm are the smallest among these algorithms.
In summary, compared with the other algorithms for the Fm|blocking|C max schedulingproblem,
the algorithm proposed in this study does better in both exploration and exploitation. Therefore,
it can achieve more outperforming solutions.
5.2.6. Non-parametric testing in the value of ARPD
To evaluate whether the differences in the value of ARPD between the algorithm proposed in this
study and the comparative ones are significant, the Mann–Whitney U distribution test, a non-
parametric testing method, was conducted. Table 7 lists the experimental results; the symbols ‘+’
and ‘−’ in the table denote that the proposed algorithm is significantly superior and inferior to
the comparative method, respectively, whereas the symbol ‘0’ indicates that there is no significant
difference between them.
Table 7 reports that: (1) the proposed algorithm is significantly inferior to HDDE, DABC, EDEc
and IABC for the instance of 20 × 5; (2) for the 20 × 10 and 20 × 20 instances, the proposed
algorithm is not significantly different from the comparative algorithms except for TS + M; (3)
for the 100 × 5 instance, the proposed algorithm is inferior to EDEc; (4) there is no significant
difference between DE-ABC and IABC for the 500 × 20 instance; and (5) except for the abovecases, the proposed algorithm is significantly superior to TS + M, HDDE, DPSOsvns, DABC,
EDEc and IABC.
From the above experimental results, it can be concluded that the proposed algorithm is
significantly superior to the comparative ones for most instances.
Table 7. Non-parametric testing results in the average relative percentage difference (ARPD) value.
DE-ABC vs TS + M HDDE DPSOsvns DABC EDEc IABC
20 × 5 + − + − − −
20 × 10 + 0 0 0 0 020 × 20 + 0 0 0 0 0
50 × 5 + + + + 0 +
50 × 10 + + + + + +
50 × 20 + + + + + +
100 × 5 + + + + − +
100 × 10 + + + + + +
100 × 20 + + + + + +
200 × 10 + + + + + +
200 × 20 + + + + + +
500 × 20 + + + + + 0
–0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 14.1
4.15
4.2
4.25
4.3
Parameter pmu
A R P D
Figure 9. Influence of parameter pmu on the average relative percentage difference (ARPD).
5.2.7. Sensitivity analysis on parameters pmu, pls and pc
There are three important parameters, pmu, pc and pls, in the proposed algorithm. To investigate
the influences of these parameters on the performances of DE-ABC, their values were changed
from 0 to 1.0 with a step size of 0.1, and the corresponding values of ARPD were obtained and
are shown in Figures 9–11. In these figures, the horizontal coordinate denotes the value of a
parameter, and the vertical coordinate represents the average value of ARPD for 120 instances.
Figure 9 illustrates that: (1) the trajectory tendency is relatively stable when the value of pmu
varies in the range of [0, 0.1]; (2) the value of ARPD gradually reduces to a low level when thevalue of pmu changes from 0.1 to 0.2 and from 0.3 to 0.8; and (3) when pmu is equal to 0.9, the
ARPD value reaches the largest value, 4.22. It can be concluded that the parameter pmu has no
evident influence on the value of ARPD of the proposed algorithm. Therefore, in this study, the
equivalently, the mutation operator works with the same probability; and (2) if pc = 1, then the
value of ARPD is the smallest, indicating that only the crossover operator is used to generate a
new solution based on the current reference one, resulting in trapping into local optima of the
optimization problem. Thus, the value of pc is set as 0.1 in this study.
Figure 11 demonstrates that: (1) when the value of pls is equal to 0, suggesting that the selected
solutions do not undergo the local search at all, the proposed algorithm will have a bad perfor-
mance; and (2) the larger the value of pls, the smaller the value of ARPD obtained by the proposed
algorithm. This is the reason why the selected solutions will perform the local search with a large
probability, which needs to spend a long time and loses opportunities to generate promising solu-
tions by a number of iterations. Therefore, an appropriate value of pls leading to a good ARPD is
set as 0.2.
6. Conclusions
Since the BFS scheduling problem plays a key role in real-world applications, it is necessary to
develop effective methods for this problem. In recent years, both ABC and DE have proven to be
effective algorithms for solving the BFS scheduling problem. Thus, a novel algorithm, DE-ABC,
is presented in this study by incorporating the merits of DDE with those of DABC to solve the
BFS problem with makespan criterion. First, the mutation and crossover operators with powerful
exploration are adopted to generate solutions in the employed bee stage, and then the insert or swap
operator based on the self-adaptive strategy is proposed to modify the selected solutions in the
onlooker bee stage. Finally, an efficient local search operator based on the insert neighbourhood
is designed to improve the algorithm’s capability in exploitation.
The performances of the proposed algorithm in this article are measured on a set of 120benchmark instances proposed by Taillard. The experimental results demonstrate the superiority
of the proposed algorithm in terms of the ARPD indicator by comparison with the results yielded
by some algorithms presented in the literature, such as TS + M, DPSOsvns, DABC, HDDE, EDEc
and IABC.
It is worth mentioning that the excellent performance of the proposed algorithm in exploration
and exploitation may be attributed to the combination of DDE, the insert or swap operator based
on the self-adaptive strategy and the local search. Future work could apply the proposed algorithm
to scheduling problems with other criteria and extend the ideas proposed in this study to multi-
objective scheduling problems.
Funding
This researchis jointly supported by the NationalNaturalScience Foundation of China [grant no. 61375067]; FundamentalResearch Funds for the Central Universities [grant no. 2013XK09]
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