2. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 2 of 20
Central Kitchen (CK) used to store raw materials from suppliers and would be distri-
buted to each outlet. The business process in PT XYZ is every night, each outlet sends a
purchase order to CK, and on the next day they will send an employee to picks the raw
materials up from the CK.
The problem that PT XYZ have is inefficiency in the current distribution method. It
contributes to the high distribution cost that the company should spend because each
outlet conducts two to ten times of trip every day. Thus, PT XYZ wants to change the
distribution method from each outlet to pick the raw materials from the CK (operator
pickup) into the direct delivery method from CK to each outlet (direct shipping).
By implementing the new distribution method, PT XYZ have to buy operational
vehicles to distribute raw materials from the CK to each outlet. The new distribution
method design will be influenced by operational vehicles’ efficiency, where they can
distribute raw materials with minimal cost. Hence, PT XYZ needs to determine the most
appropriate distribution route to minimize transportation costs expensed.
In conducting the optimum route determination strategy in PT XYZ, a model for
finding the most appropriate solution is needed. Vehicle Routing Problem (VRP) is the
most appropriate model to use for problems related to route determination. VRP model
can be defined as finding the optimal route from a depot to several customers in scattered
areas and with different demand numbers. The VRP Model has several variations, which
are grouped based on the limitations they have. The most appropriate completion model
for the problem in PT XYZ where CK and outlets have their service time in delivery and
receiving was the Vehicle Routing Problem with Time Windows (VRPTW).
VRPTW model is used to schedule trips from a group of vehicles with limited ca-
pacity and travel time from the main depot to all customers in different locations, with
demand and service time in particular (Nugraha and Mahmudy, 2015). Penentlitian se-
belumnya terkait VRPTW for restaurant chain.
Theoretically, VRPTW is an NP-hard problem, where solving the problem requires
complex computational effort and long computation time [2]. So, one method that can be
used to solve the NP-hard problem by using the metaheuristic method. The metaheuris-
tic method was created to solve high-complexity problems and generate a near-optimum
solution [2].
Solving optimization problem using metaheuristic algorithms tend to increase every
year. One of the recent metaheuristic methods that many researchers developed is Sym-
biotic Organisms Search (SOS) algorithm. Another metaheuristic algorithm commonly
used to solve determination optimization problems is Particle Swarm Optimization
(PSO). SOS and PSO have the same solution-seeking characteristics inspired by natural
principles of living things and population-based approaches. Due to the same characte-
ristics of SOS and PSO algorithms, many researchers evaluated and tested the solution
quality generated from both algorithms.
The comparison of performance evaluation between SOS and PSO algorithms was
conducted by Yu et al. [3], which applied SOS and PSO algorithms on the CVRP problem.
There was also research by Umam et al. [4] that modified the SOS algorithm for the TSP
problem and compared the generated solution quality with the solution obtained from
the PSO algorithm. Another research that tested both algorithms’ performance is by Pa-
rayogo et al. [5] in their research regarding the layout determination of construction
project facility based on working mileage.
This research aimed to conduct performance quality testing between SOS and PSO
algorithms in solving the VRPTW problem based on the research background. The algo-
rithm with the best solution performance will be implemented in the company’s route
determination. Besides, this research also conducted a feasibility analysis using the
capital budgeting method to discover the feasibility of the new distribution method plan
to be implemented in the company’s system.
2. Deskripsi Permasalahan
3. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW
Metode pendistribusian bahan makanan dari Central Kitchen (CK) ke ma
ing-masing outlet di PT XYZ yang kurang optimal menjadi sebuah permasalahan yang
perlu diperbaiki. Permasalahan inefisiensi dalam metode pendistribusian di PT XYZ
menyebabkan tingginya biaya distribusi yang perlu dikeluarkan. Hal ini dikarenakan
dalam pengam
melakukan dua sampai sepuluh kali perjalanan setiap harinya. Selain itu,terjadinya k
terlambatan dalam pengambilan bahan makanan oleh pegawai dari masing
outlet membuat kurang opti
Permasalahan lain terkait metode distribusi yang saat ini diterapkan oleh PT XYZ
yaitu ketidaksesuaian data barang yang ada dalam sistem inventory dengan barang yang
disimpan. Hal ini terjadi dikarenakan, pe
melebihi waktu pelayanan CK.
han-permasalahan terkait sistem pendistribusian yang kurang optimal, PT XYZ ingin
menerapakan sebuah kebijakan baru. Dimana kebijakan baru t
pengiriman bahan makanan yang diambil oleh karyawan masing
tor pickup) menjadi CK yang mengirimkan secara langsung bahan makanan ke ma
ing-masing outlet (direct shipping). Dengan kebijakan yang baru tersebut, PT
membeli kendaraan operasional perusahaan yang digunakan untuk mendistribusikan
bahan makanan dari CK ke masing
, x FOR PEER REVIEW
Metode pendistribusian bahan makanan dari Central Kitchen (CK) ke ma
masing outlet di PT XYZ yang kurang optimal menjadi sebuah permasalahan yang
perlu diperbaiki. Permasalahan inefisiensi dalam metode pendistribusian di PT XYZ
menyebabkan tingginya biaya distribusi yang perlu dikeluarkan. Hal ini dikarenakan
dalam pengambilan bahan makanan dari CK ke masing-masing outlet, kendaraan harus
melakukan dua sampai sepuluh kali perjalanan setiap harinya. Selain itu,terjadinya k
terlambatan dalam pengambilan bahan makanan oleh pegawai dari masing
outlet membuat kurang optimalnya waktu pegawai dalam bekerja satu harinya.
Permasalahan lain terkait metode distribusi yang saat ini diterapkan oleh PT XYZ
ketidaksesuaian data barang yang ada dalam sistem inventory dengan barang yang
disimpan. Hal ini terjadi dikarenakan, pegawai dari masing-masing outlet datang ke CK
melebihi waktu pelayanan CK. Oleh karena itu, untuk mengatasi permasal
permasalahan terkait sistem pendistribusian yang kurang optimal, PT XYZ ingin
menerapakan sebuah kebijakan baru. Dimana kebijakan baru tersebut mengganti metode
pengiriman bahan makanan yang diambil oleh karyawan masing
tor pickup) menjadi CK yang mengirimkan secara langsung bahan makanan ke ma
masing outlet (direct shipping). Dengan kebijakan yang baru tersebut, PT
membeli kendaraan operasional perusahaan yang digunakan untuk mendistribusikan
bahan makanan dari CK ke masing-masing outlet.
Illustrate Old Distribution Method
3 of 20
Metode pendistribusian bahan makanan dari Central Kitchen (CK) ke mas-
masing outlet di PT XYZ yang kurang optimal menjadi sebuah permasalahan yang
perlu diperbaiki. Permasalahan inefisiensi dalam metode pendistribusian di PT XYZ
menyebabkan tingginya biaya distribusi yang perlu dikeluarkan. Hal ini dikarenakan
masing outlet, kendaraan harus
melakukan dua sampai sepuluh kali perjalanan setiap harinya. Selain itu,terjadinya ke-
terlambatan dalam pengambilan bahan makanan oleh pegawai dari masing-masing
malnya waktu pegawai dalam bekerja satu harinya.
Permasalahan lain terkait metode distribusi yang saat ini diterapkan oleh PT XYZ
ketidaksesuaian data barang yang ada dalam sistem inventory dengan barang yang
masing outlet datang ke CK
Oleh karena itu, untuk mengatasi permasala-
permasalahan terkait sistem pendistribusian yang kurang optimal, PT XYZ ingin
ersebut mengganti metode
pengiriman bahan makanan yang diambil oleh karyawan masing-masing outlet (opera-
tor pickup) menjadi CK yang mengirimkan secara langsung bahan makanan ke mas-
masing outlet (direct shipping). Dengan kebijakan yang baru tersebut, PT XYZ ingin
membeli kendaraan operasional perusahaan yang digunakan untuk mendistribusikan
4. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW
Dalam melakukan pembelian kendaraan
makanan, PT XYZ memiliki beberapa faktor pertimbangan dalam memilih moda
trasnsportasi yang paling tepat untuk diterapkan dalam operasional perusahaan. Faktor
pertama yaitu total biaya investasi, perusahaan menetap
vestasi yang dikeluarkan tidak lebih dari Rp 120.000.000. Faktor kedua yaitu fleksibilitas
operasional kendaraan, perusahaan menginginkan moda trasnsportasi yang dapat be
gerak dengan cepat dan dapat menyesuaikan dengan berbagai
memiliki biaya bahan bakar yang rendah. Faktor yang terakhir yaitu penggunaan lahan
parkir karena tidak semua outlet memiliki lahan parkir untuk kendaraan yang luas, s
hingga hal ini yang menjadi salah satu faktor pertimbangan dala
transportasi.
Berdasarkan faktor
transportasi yang tepat untuk digunakan yaitu kendaraan roda dua dengan box peng
riman berkapasitas 50kg dan kendaraan roda tiga berkapasitas 250kg. Ba
kendaraan yang nantinya digunakan juga mengikuti besarnya permintaan dari ma
ing-masing outlet untuk tujuh hari pengiriman. Dimana besarnya permintaan outlet
untuk tujuh hari pengiriman yaitu 207kg sampai dengan 295kg. Sehingga jumlah ke
daraan yang akan dibeli untuk memenuhi permintaan semua outlet yaitu sebanyak
enam kendaraan motor roda dua dan dua kendaraan motor roda tiga.
Untuk meminimumkan biaya trannportasi yang nantinya dikeluarkan oleh PT XYZ,
pada penelitian ini akan dilakukan den
kan pendistribusian bahan makanan. Pencarian rute yang optimal nantinya akan
menggunakan model Vehicle Routing Problem with Time Windows (VRPTW) dengan
metode metaheuristik yaitu algoritma SOS dan PSO sebagai met
Setalah mengetahui rute serta biaya transportasi yang paling optimal, penelitian ini juga
akan membahas terkait analisis kelayakan investasi dari kendaraan operasional yang
akan dibeli.
Berdasarkan penjelasan di atas, untuk dapat menera
yang baru di PT XYZ, maka dibuat dua skenario pengiriman bahan makanan dengan j
nis kenadaraan yang berbeda.
1. Skenario Pengiriman Pertama
, x FOR PEER REVIEW
Illustrate New Distribution Method
Dalam melakukan pembelian kendaraan operasional untuk mendistribusikan bahan
makanan, PT XYZ memiliki beberapa faktor pertimbangan dalam memilih moda
trasnsportasi yang paling tepat untuk diterapkan dalam operasional perusahaan. Faktor
pertama yaitu total biaya investasi, perusahaan menetapkan bahwa besarnya biaya i
vestasi yang dikeluarkan tidak lebih dari Rp 120.000.000. Faktor kedua yaitu fleksibilitas
operasional kendaraan, perusahaan menginginkan moda trasnsportasi yang dapat be
gerak dengan cepat dan dapat menyesuaikan dengan berbagai kondisi pengiriman serta
memiliki biaya bahan bakar yang rendah. Faktor yang terakhir yaitu penggunaan lahan
parkir karena tidak semua outlet memiliki lahan parkir untuk kendaraan yang luas, s
hingga hal ini yang menjadi salah satu faktor pertimbangan dala
Berdasarkan faktor-faktor yang dipertimbangkan oleh perusahaan, maka moda
transportasi yang tepat untuk digunakan yaitu kendaraan roda dua dengan box peng
riman berkapasitas 50kg dan kendaraan roda tiga berkapasitas 250kg. Ba
kendaraan yang nantinya digunakan juga mengikuti besarnya permintaan dari ma
masing outlet untuk tujuh hari pengiriman. Dimana besarnya permintaan outlet
untuk tujuh hari pengiriman yaitu 207kg sampai dengan 295kg. Sehingga jumlah ke
aan yang akan dibeli untuk memenuhi permintaan semua outlet yaitu sebanyak
enam kendaraan motor roda dua dan dua kendaraan motor roda tiga.
Untuk meminimumkan biaya trannportasi yang nantinya dikeluarkan oleh PT XYZ,
pada penelitian ini akan dilakukan dengan pencarian rute yang optimal untuk melak
kan pendistribusian bahan makanan. Pencarian rute yang optimal nantinya akan
menggunakan model Vehicle Routing Problem with Time Windows (VRPTW) dengan
metode metaheuristik yaitu algoritma SOS dan PSO sebagai met
Setalah mengetahui rute serta biaya transportasi yang paling optimal, penelitian ini juga
akan membahas terkait analisis kelayakan investasi dari kendaraan operasional yang
Berdasarkan penjelasan di atas, untuk dapat menerapkan kebijakan pendistribusian
yang baru di PT XYZ, maka dibuat dua skenario pengiriman bahan makanan dengan j
nis kenadaraan yang berbeda.
Skenario Pengiriman Pertama
4 of 20
operasional untuk mendistribusikan bahan
makanan, PT XYZ memiliki beberapa faktor pertimbangan dalam memilih moda
trasnsportasi yang paling tepat untuk diterapkan dalam operasional perusahaan. Faktor
kan bahwa besarnya biaya in-
vestasi yang dikeluarkan tidak lebih dari Rp 120.000.000. Faktor kedua yaitu fleksibilitas
operasional kendaraan, perusahaan menginginkan moda trasnsportasi yang dapat ber-
kondisi pengiriman serta
memiliki biaya bahan bakar yang rendah. Faktor yang terakhir yaitu penggunaan lahan
parkir karena tidak semua outlet memiliki lahan parkir untuk kendaraan yang luas, se-
hingga hal ini yang menjadi salah satu faktor pertimbangan dalam pemilihan moda
faktor yang dipertimbangkan oleh perusahaan, maka moda
transportasi yang tepat untuk digunakan yaitu kendaraan roda dua dengan box pengi-
riman berkapasitas 50kg dan kendaraan roda tiga berkapasitas 250kg. Banyaknya jumlah
kendaraan yang nantinya digunakan juga mengikuti besarnya permintaan dari mas-
masing outlet untuk tujuh hari pengiriman. Dimana besarnya permintaan outlet
untuk tujuh hari pengiriman yaitu 207kg sampai dengan 295kg. Sehingga jumlah ken-
aan yang akan dibeli untuk memenuhi permintaan semua outlet yaitu sebanyak
enam kendaraan motor roda dua dan dua kendaraan motor roda tiga.
Untuk meminimumkan biaya trannportasi yang nantinya dikeluarkan oleh PT XYZ,
gan pencarian rute yang optimal untuk melaku-
kan pendistribusian bahan makanan. Pencarian rute yang optimal nantinya akan
menggunakan model Vehicle Routing Problem with Time Windows (VRPTW) dengan
metode metaheuristik yaitu algoritma SOS dan PSO sebagai metode pendekatannya.
Setalah mengetahui rute serta biaya transportasi yang paling optimal, penelitian ini juga
akan membahas terkait analisis kelayakan investasi dari kendaraan operasional yang
pkan kebijakan pendistribusian
yang baru di PT XYZ, maka dibuat dua skenario pengiriman bahan makanan dengan je-
5. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 5 of 20
Pada skenario pertama, pengiriman dilakukan dengan menggunakan kendaraan
roda dua yaitu motor dengan tambahan tas box pengiriman sebagai media angkutnya.
Skenario pengiriman pertama memiliki frekuensi pengiriman sebanyak enam kali dalam
satu harinya. Jadwal pengiriman ini terbagi menjadi pengiriman pagi 1, pengiriman pagi
2, pengiriman siang 1, pengiriman siang 2, pengiriman sore 1, dan pengiriman sore 2.
Data yang digunakan dalam skenario pengiriman pertama yaitu merupakan data large
instance 50kg. Dimana pada data large instance 50kg, permintaan bahan makanan yang
perlu dikirimkan oleh Central Kitchen ke masing-masing outlet akan dipecah berdasar-
kan waktu pengirimannya. Hal ini dilakukan karena dalam CK sendiri, tidak semua
bahan makanan dapat dipersiapkan pada pengiriman pertama. Sehingga apabila pengi-
riman ke masing-masing outlet menunggu bahan makanan yang belum dipersiapkan,
maka yang terjadi adalah terjadinya kekurangan bahan makanan lainnya yang dibu-
tuhkan oleh masing-masing outlet. Oleh karena itulah dibuat sebuah jadwal pengiriman
bahan makanan menjadi enam kali dalam seharinya agar bahan-bahan makanan yang
tidak dapat dikirimkan pada pengiriman awal, dapat dikirimkan pada pengiriman se-
lanjutnya.
2. Skenario Pengiriman Kedua
Pada skenario kedua, pengiriman dilakukan dengan menggunakan kendaraan
motor roda tiga dengan kapasitas angkut sebesar 250kg. Data yang digunakan dalam
skenario pengiriman kedua yaitu data large instance 250kg. Skenario pengiriman kedua
juga memiliki frekuensi pengiriman yang sama dengan pengiriman pertama, dimana
terjadi dua kali pengiriman di setiap pagi, siang, dan sore. Hal yang membedakan ske-
nario pengiriman pertama dan skenario pengiriman kedua yaitu dari sisi operasional
bahan bakar dan besarnya biaya investasi yang perlu dikeluarkan. Dengan adanya dua
skenario pengiriman yang ada, nantinya dapat dibandingkan skenario mana yang
menghasilkan keuntungan yang lebih baik untuk PT XYZ dibandingkan dengan skena-
rio lainnya.
3. Metodology
Dalam melakukan penelitian ini, tahapan-tahapan yang dilakukan dimulai dengan
mengidentifikasi permasalahan yang terjadi pada objek penelitian yaitu PT XYZ. Taha-
pan selanjutnya yaitu menentukan tujuan penelitian yang ingin dicapai dari permasala-
han yang terjadi. Setelah menentukan tujuan yang dicapai, selanjutnya melakukan studi
pustaka pada penelitian sebelumnya terkait solusi apa saya yang bisa dilakukan untuk
menyelesaikan permasalahan yang terjadi.
Membangun model matematis matematis menjadi salah satu tahapan penting yang
dilakukan pada penelitian ini. Hal ini dilakukan untuk memastikan, apakah model pe-
nyelesaian yang digunakan yaitu VRPTW sudah sesuai dan merepresentasikan dengan
permasalahan yang terjadi. Setelah model dinyatakan sesuai dengan permasalahan,
maka sebelum XXXX
3.1. Vehicle Routing Problem with Time Windows
Vehicle Routing Problem or commonly referred to as VRP, is a transportation model
problem that aims to solve the problem of determining the route by using several ve-
hicles and serving several customers in several different locations, where each customer
has their demands, and the vehicles that used to transport has it is own the vehicle ca-
pacity. The VRP model has several development model variations that adjusted to the
constraints and complexities of a problem.
Vehicle Routing Problem with Time Windows (VRPTW) is one of the VRP variations
that consider vehicle capacity limit and service time interval (time windows) in each
customer. VRPTW aims to minimize the total transportation cost by considering the ve-
hicle’s cost and traveling time matrixes. In the VRPTW model, there are two service time
types to can be used, i.e., hard time windows and soft time windows. However, in this
6. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 6 of 20
research, the VRPTW model used was the hard time windows. In this model, when the
vehicle comes after the service time, then customers cannot serve the vehicle. This
VRPTW model fits with the problem in PT XYZ, because if the vehicle comes after the
service time, there are no employees who were serving it.
3.2. Model Formulation
The mathematical model formulation used in this research is the model of Vehicle
Routing Problem with Time Windows (VRPTW) that developed by Kallehauge in 2001
[6]. This model has purpose to minimize the total transportation costs with time windows
at each customer. The VRPTW mathematical model has a mathematical notation as fol-
lows:
: a set of vehicles with the same capacity
: a set of customers
: a set of points consisting customers and depots
: vehicle capacity
k: vehicle
i: customers demand
Cij: transportation costs from nodes i to nodes j
ij: travel timefrom nodes i to nodes j
Sik: starting timeof service at customers i
i: earliest time of service at customers i
i: latest time of service at customers i
The decision variable of the VRPTW mathematical model is:
7. 1, if there is a vehicle trip from i to j on route k
0, if there is no vehicle trip from i to j on route k
$
Then the objective function is:
min = '
22. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 7 of 20
Based on the mathematical formulation above, equation 1 is an objective function of
the model to minimize travel costs. Equation 2 stated that each customer is visited once.
Equation 3 shows the limitation that a vehicle may not carry more than the vehicle's
capacity. Equation 4 shows that each vehicle starts from a depot. Equation 5 shows that
after visiting a customer, the vehicle will leave that customer and visit the next customer,
and equation 6 states that each vehicle will end up at the depot.Equation 7 is used to
express the relationship between the time of departure from customers and the time of
travel to the next customer. Equation 8 ensures that the time windows limit of each
customer is met and equation 9 states that the decision variable xijk is binary.
Based on the mathematical model above it is known that equation 7 is nonlinear,
therefore it needs to be changed to linear to verify the model. The linear equation is:
@
25. ∀., C ∈ , ∀2 ∈ (10)
Where constantan Mij can be derived tomax J
+
− K, (., C) ∈ L.
3.3. Metaheuristic Algorithm
3.3.1. SOS Algorithm
The SOS algorithm is an optimization technique adopted from the inter-organism
relationship pattern in its survival and proliferation [7]. Solution-seeking on the SOS al-
gorithm begins with the initial population, the so-called ecosystem, consisting of several
randomized individuals. These individuals will later pass three iterative seeking stages
to generate an optimum solution variable.
At each stage, each individual will interact randomly with one another to generate
solutions. Interaction results on each stage will be evaluated for their objective value to
obtain the best solution. The SOS algorithm’s seeking solution process will stop when the
termination criteria are met. The pseudocode from the Symbiotic Organisms Search al-
gorithm used in this research is presented in Figure X.
BF= = (1 + round (rand(0,1))
Step 1: Ecosystem Initialization
Step 2: For i = 1, 2, . . ., eco_size
Evaluate f(Xi)
Xbest = Minimum f(Xi)
If Obj (Xi) Obj (Xbest) do
Update Xbest = Xi
End if
Step 3:
Whileiteration (iter) maximum iteration (max iter) do
Fori = 1, 2, . . ., eco_size
Mutualism Phase
Select one organisme Xj randomly, where Xj ≠ Xi
Calculate benefit vector and mutual vector
BFQ = (1 + round (rand(0,1))
Mutual vector =
STSU
Q
26. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 8 of 20
Figure X Pseudocode SOS
Figure X Cont.
XWXYZ = XW + rand(0,1) ∗ (XY]^ − X_)
X`aba]W^Y = rand (0,1) ∗ (UB − LB) + LB
Comensalism Phase
Select one organisme Xj randomly, where Xj ≠ Xi
Calculate Xinew
Decode Xinew
Evaluate f(Xinew)
If Obj Xinew Obj Xi do
Update Xi = Xinew
End If
Parasitism Phase
Select one organisme Xj randomly, where Xj ≠ Xi
Generate Xparasite from organism Xi
Generate r = random (0,1)
r parasite_force
Mutation Xi uses a random number with a range of [ub,lb]
Decode Xparasite Xparasite dan Xj
Evaluate f(Xparasite) and f(Xjnew)
If Obj Xparasite Obj Xj do
Update Xj = Xparasite
End If
End for
End while
27. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 9 of 20
3.3.2. PSO Algorithm
The solution-seeking procedure on PSO was conducted by a population comprised
of several particles. Because PSO uses stochastics data, then the population within has to
be raised using random numbers with the lowest value and highest value limitations. In
seeking solutions, each particle conducts searching in the search space to find its par-
ticle's best position (local best) and the best position of all populations (global best).
Moving particles will be searching in the search space using dynamic velocity that tends
to move to the best searching area.
Each particle executes the best position-seeking process in several determined par-
ticular iteration. On each iteration, solutions represented by the particle position were
evaluated for their performance by entering the solution to the fitness function [8]. The
pseudocode from the Particle Swarm Optimization algorithm in this research is pre-
sented in Figure X.
Figure X Pseudocode PSO Algorithm
e
(f=) = e
(f) +
(f=)
Step 1 :
For each particle i : 1, 2, …N
Random initialization Xi
Random initialization Vi (or just set Vi to zero)
Evaluate the fitness of particle i, f(xi)
Evaluate Pbest and Gbest
End For
Step 2 :
While iteration (iter) maximum iteration (max iter)do
For each particle i : 1, 2, …N
Update Velocities with
(f=) = g
(f) + h='=?ij@
(f) − e
(f)B + hQ'Q?kj@
(f) − e
(f)B
Update Position with
Evaluate the fitness of particle i, f(xi)
If Pbest(t+1) Pbest(t) do
Pbest(t) = Pbest(t+1)
End If
Gbest(t+1) = small value in Pbest
If Gbest(t+1) Gbest(t) do
Gbest(t) = Gbest(t+1)
End For
End While
28. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW
3.4. Solution Representation
Solution representation determination is an important process in implementing a
metaheuristic algorithm. It is because the solution representation is the illustration r
presentation of the generated
creating a route to distribute raw materials from the CK to each outlet by not violating
the vehicle capacity limit and service time on each outlet.
The route began by vehicles departing from the
nodes that have demand less than the vehicle capacity. Another limitation of vehicles’
starting time on each node is also mandatory besides the vehicle capacity. If the vehicle
came after the outlet’s service time, the
Therefore, the vehicle could not be served on that node and had to find another node or
go back to the depot. One of the solution representation examples in this research is
presented in Figure X.
3.5. Feasibility Study Analysis
Feasibility study analysis is a procedure to assess, measure, and analyze the feas
bility of a policy plan or project to be executed [10]. In conducting a feasibility study,
there are three thin
and capital budgeting analysis. There are three methods to evaluate an investment’s fe
sibility in the capital budgeting analysis, namely NPV, PI, and PP. Solution represent
tion determination is an important process in implementing a metaheuristic algorithm. It
is because the solution representation is the illustration representation of the generated
solution [9]. The solution
raw materials from the CK to each outlet by not violating the vehicle capacity limit and
service time on each outlet.
3.5.1. Net Present Value (NPV) Model
It is a technique to estimate the company's generated profit in the future if we invest with t
current monetary value. The NPV calculation is as follows:
Where:
NPV : Net Present Value
Lf : Cash flow
i : Interest rate used
t : Project’s economist life, started from the initial stage to the end of
n : Reviewed project’s life
3.5.2. Profitability Index (PI) Method
It is a technique to estimate a project’s feasibility by comparing its net profit value
with the initial investment value. The profitability index calculation is as
, x FOR PEER REVIEW
Solution Representation
Solution representation determination is an important process in implementing a
metaheuristic algorithm. It is because the solution representation is the illustration r
presentation of the generated solution [9]. The solution-seeking in this research was by
creating a route to distribute raw materials from the CK to each outlet by not violating
the vehicle capacity limit and service time on each outlet.
The route began by vehicles departing from the depot, and then each vehicle went to
nodes that have demand less than the vehicle capacity. Another limitation of vehicles’
starting time on each node is also mandatory besides the vehicle capacity. If the vehicle
came after the outlet’s service time, the nodes violated the service time limitation.
Therefore, the vehicle could not be served on that node and had to find another node or
go back to the depot. One of the solution representation examples in this research is
presented in Figure X.
Figure X Representation Solution VRPTW Model
Feasibility Study Analysis
Feasibility study analysis is a procedure to assess, measure, and analyze the feas
bility of a policy plan or project to be executed [10]. In conducting a feasibility study,
there are three things to be considered, i.e., financial analysis, perceived benefit analysis,
and capital budgeting analysis. There are three methods to evaluate an investment’s fe
sibility in the capital budgeting analysis, namely NPV, PI, and PP. Solution represent
termination is an important process in implementing a metaheuristic algorithm. It
is because the solution representation is the illustration representation of the generated
solution [9]. The solution-seeking in this research was by creating a route to dist
raw materials from the CK to each outlet by not violating the vehicle capacity limit and
service time on each outlet.
Net Present Value (NPV) Model
It is a technique to estimate the company's generated profit in the future if we invest with t
current monetary value. The NPV calculation is as follows:
i =
Lf
(1 + .)f
;
fl5
(11)
Net Present Value
Cash flow on period t
: Interest rate used
: Project’s economist life, started from the initial stage to the end of
: Reviewed project’s life
Profitability Index (PI) Method
It is a technique to estimate a project’s feasibility by comparing its net profit value
with the initial investment value. The profitability index calculation is as
10 of 20
Solution representation determination is an important process in implementing a
metaheuristic algorithm. It is because the solution representation is the illustration re-
seeking in this research was by
creating a route to distribute raw materials from the CK to each outlet by not violating
depot, and then each vehicle went to
nodes that have demand less than the vehicle capacity. Another limitation of vehicles’
starting time on each node is also mandatory besides the vehicle capacity. If the vehicle
nodes violated the service time limitation.
Therefore, the vehicle could not be served on that node and had to find another node or
go back to the depot. One of the solution representation examples in this research is
entation Solution VRPTW Model
Feasibility study analysis is a procedure to assess, measure, and analyze the feasi-
bility of a policy plan or project to be executed [10]. In conducting a feasibility study,
gs to be considered, i.e., financial analysis, perceived benefit analysis,
and capital budgeting analysis. There are three methods to evaluate an investment’s fea-
sibility in the capital budgeting analysis, namely NPV, PI, and PP. Solution representa-
termination is an important process in implementing a metaheuristic algorithm. It
is because the solution representation is the illustration representation of the generated
seeking in this research was by creating a route to distribute
raw materials from the CK to each outlet by not violating the vehicle capacity limit and
It is a technique to estimate the company's generated profit in the future if we invest with the
: Project’s economist life, started from the initial stage to the end of project’s life
It is a technique to estimate a project’s feasibility by comparing its net profit value
with the initial investment value. The profitability index calculation is as follows:
29. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 11 of 20
PI =
PV of future cash plow
PV of investment
(12)
Where:
PI : Profitability index
PV of future cash flow : Present value of future cash flow
PV of investment : Initial Investment
3.5.3. Payback Period (PP) Method
It is a technique used to assess the period of return on investment. The payback pe-
riod calculation is as follows:
PP =
Cost of Investment
Annual cashplow
x 1 year (13)
Where:
PP : Payback period
4. Result and Discussion
Data used in this research were divided into two, i.e., small instance and large in-
stance data. The small instance data shows data for one-time delivery frequency, while
the large instance data shows delivery scenario data in a day. The large instance data it-
self is data processed following the delivery frequency to be implemented. This data was
made by dividing each customer’s demand based on the delivery time and adjusted to
vehicle capacity. In this research, the large instance data was categorized into two, i.e.,
large instance 50 kg and large instance 250 kg. The large instance 50 kg was the data used
in the first delivery scenario using two-wheeled motor vehicles and a delivery box of 50
kg capacity. Meanwhile, the large instance 250 kg data was used in the second scenario
using three-wheeled motor vehicles with a maximum capacity 250 kg.
The data processing in this research used AMPL software with a GUROBI solver to
verify the mathematical model. Meanwhile, for SOS and PSO metaheuristic methods
program, Visual Studio of 2019 with C# programming language was used. Another
software used was SPSS 16.0 to test statistical analysis. The computer used in this re-
search was Lenovo C340 with specifications of intel core i3-10110U processor, RAM 8 GB,
and system windows 10 64-bit.
4.1. Verification and Validation Model
Model verification was conducted to ensure that the objective function and con-
straints of the model are mathematically accurate and logically consistent. Meanwhile,
model validation was conducted to ensure that the mathematical model computation
will generate the same output as manual calculation. Model verification and validation
were conducted using the AMPL software, which declared that the model was verified
and validated. The verification was proven by the absence of sub-routes or errors on the
generated output. The model was also validated because it had the same value as the
results of manual calculation. The verification and validation processes for the small in-
stance data produce an optimum solution with an objective value of 4240.
4.2. Parameter Tuning
Parameter tuning was conducted to discover the parameter combination that gene-
rates the best solution quality with short computation times. In this research, parameter
value was determined before the algorithm was running, so-called off-line tuning. The
parameter tuning method used in this research was the One Factor at A Time (OFAT),
where one parameter will be tested for each value and assuming that other untested pa-
30. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 12 of 20
rameters have fixed values. Parameter value determination for both metaheuristic me-
thods was adopted from a literature review of previous research. Parameter values used
in this research are shown in Table 1.
Table
1.Parameter
Values of
SOS and
PSO Algo-
rithms
All parameter values in Table 1 were combined with each other to be analyzed for
their parameter sensitivity. The parameter sensitivity analysis was made to discover the
effect of a parameter on its solution quality and computation time length. The result of
sensitivity analysis is discovering the best value of each parameter in solving the VRPTW
problem.
Based on the sensitivity analysis results, the best parameter value in the SOS algo-
rithm for maxiter value is 1000, eco size 50, and parasite force (pf) 0.7. Meanwhile, the
PSO algorithm has the best maxiter value 500, inertia weight (w) 1, swarm size (N) 20,
and cognitive and social factors with the same value 2.
4.3. Verification and Validation Algorithm
By using the best parameter value combination, the next step was to verify and va-
lidate algorithms. Algorithm verification and validation were conducted by comparing
the results of the objective values obtained from SOS and PSO algorithms with the objec-
tive values from the exact method. The verification and validation results are shown in
Table 2. The table shows that SOS and PSO algorithms can generate the same objective
values as a result of the exact method.
Table 2.Computation Results of SOS and PSO Algorithms for the Small Instance Data
Instance
Exact Method SOS Algorithm PSO Algorithm
Objective Value Objective Value Objective Value
Small - 1 4240 4240 4240
Small - 2 4240 4240 4240
Small - 3 4240 4240 4240
Small - 4 4240 4240 4240
Small - 5 4240 4240 4240
Small - 6 4240 4240 4240
Small - 7 4240 4240 4240
Algorithm Parameter Value
SOS
Maxiter 500 1000 1500
Eco Size 25 50 75
Parasite Force (pf) 0.7 0.8 0.9
PSO
Maxiter 500 1000
Inertia Weight (w) 0.25 0.5 1
Swarm Size (N) 20 40 80
Cognitive Factor 1 2
Social Factor 1 2
31. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 13 of 20
4.4. Computational Result
Based on algorithm verification and validation results, it can be known that SOS and
PSO algorithms can generate an optimum solution for the small instance data. Therefore,
these two algorithms can be used to solve the VRPTW problem in the distribution prob-
lem of PT XYZ. The results of SOS and PSO algorithms using the best parameter combi-
nation are shown in Table 3 and Table 4.
Table 3.Computational Result of SOS and PSO Algorithms for Large Instance 50 kg
Instance
SOS PSO
Best
Obj.
Average
Obj.
CPU
Time (s)
Best
Obj.
Average
Obj.
CPU
Time (s)
Large 50 -1 7691 9639 4.82 10758 15032 1.35
Large 50 -2 13379 14470 2.67 10997 11144 1.42
Large 50 -3 12795 15129 2.77 11348 12654 1.72
Large 50 -4 13683 14943 2.46 11568 13384 1.80
Large 50 -5 11777 12620 2.41 12458 13882 1.39
Large 50 -6 11057 12643 2.63 11032 12548 1.63
Large 50 -7 12300 12913 2.75 11361 14478 2.05
Average 11812 13194 2.93 11360 13303 1.62
Table 4.Computational Result of SOS and PSO Algorithms for Large Instance 250 kg
Instance
SOS PSO
Best
Obj.
Average
Obj.
CPU
Time (s)
Best
Obj.
Average
Obj.
CPU
Time (s)
Large 250 -1 19471 21035 2.28 14823 17822 1.86
Large 250 -2 17415 19664 2.41 18486 21756 1.26
Large 250 -3 20243 23442 4.17 17952 20787 1.88
Large 250 -4 19109 23085 4.99 21763 22756 1.87
Large 250 -5 17866 19529 5.22 17801 18793 1.73
Large 250 -6 21291 22028 4.68 20009 20643 1.25
Large 250 -7 17137 18529 2.67 19407 20907 2.16
Average 18933 21045 3.77 18606 20495 1.71
4.5. Statistical Analysis
The statistical analysis test was conducted to measure the solution quality perfor-
mance generated by each metaheuristic algorithm. The purpose of the statistical analysis
test is to determine the difference in average objective values of each algorithm. Testing
using statistical analysis began by conducting the normality test, homogeneity test, and
paired t-test.
4.5.1. Normality Test
The first testing was the normality test, where it was conducted to discover that the
tested data are normally distributed. The hypothesis used in this testing were as follow:
32. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 14 of 20
H0 = Data are distributed normally
H1 = Data are not distributed normally
α = 0.05
The normality test results are shown in Table 5, showing all four tested data have a
p-value (sig.) bigger than the value of α = 0.05. It is then concluded that H0 is accepted, or
the data are distributed normally.
Table 5.Results of Normality Test for the Large Instance 50 kg Data and Large Instance 250 kg Data
Algorithm
Shapiro - Wilk
Statistic df Sig
Objective
SOS 50kg 0.882 7 0.235
PSO 50kg 0.976 7 0.939
SOS 250kg 0.934 7 0.588
PSO 250kg 0.944 7 0.680
4.5.2. Normality Test Homogeneity Test
The second performance test was the homogeneity test, it was conducted to test the
variance homogeneity of data. The hypothesis used in this test were as follow:
H0 = Data variance are homogenous
H1 = Data variance are not homogenous
α = 0.05
The homogeneity test results are shown in Table 6 and Table 7, showing all four
tested data have p-value (sig) bigger than the value of α = 0.05. The decision made is that
H0 is accepted, or the data variance is homogenous.
Table 6.Results of Homogeneity Tests of the Large Instance 50 kg Data
Objective
Levene Statistic Sig.
Based on Mean 0.618 0.447
Based on Median 0.466 0.508
Based on Median and with adjusted df 0.466 0.511
Based on trimmed mean 0.678 0.426
Table 7.Results of Homogeneity Test of the Large Instance 250 kg Data
Objective
Levene Statistic Sig.
Based on Mean 0.351 0.565
Based on Median 0.480 0.502
Based on Median and with adjusted df 0.480 0.503
Based on trimmed mean 0.371 0.554
4.5.3. Normality Test Paired T-test
The last test was the paired t-test, where it was conducted to test the parametric
difference on two paired data. The computational result of the SOS algorithm in large
instance 50 kg was paired with the computational result of the PSO algorithm in large
instance 50 kg. The paired t-test was also conducted for the computational result of the
33. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 15 of 20
large instance 250 kg SOS and the computational result of the large instance 250 kg PSO.
The hypothesis used in this research were as follow:
H0 = There is not a statistically significant difference
H1 = There is a statistically significant difference
α = 0.05
The results of the paired t-test are shown in Table 8, where pair 1, the relationship
between the large instance 50 kg data of SOS and large instance 50 kg data of PSO, has a
p-value = 0.925. Meanwhile, pair 2, the relationship between the large instance 250 kg
data of SOS and large instance 250 kg data of PSO, has a p-value = 0.525. From both pairs,
it is discovered that all p-values (sig.) are bigger than the value of α = 0.05. So it is con-
cluded that H0 is accepted. It shows there is not a statistically significant difference be-
tween the results of the SOS and PSO algorithms for both data.
Table 8.Results of Paired Samples Test for SOS and SPO Algorithms
Pair t df Sig.(2-tailed)
Pair 1 SOS 50kg - PSO 50kg -0.098 6 0.925
Pair 2 SOS 250kg - PSO 250kg 0.675 6 0.525
Based on the statistical analysis results, it can be concluded that even though there
are differences between objective values generated by SOS and PSO algorithms, with the
statistical analysis test shown, the differences are insignificant. Therefore, to discover
which algorithm generates the best solution, it is necessary to conduct a test for the
computation time.
The computational time result can be seen in Table 3 and Table 4, where the PSO
algorithm in Large Instance 50 kg and Large Instance 250 kg had shorter computational
time than the SOS algorithm. So, it can be concluded that the PSO algorithm can get the
solution that tends to optimal with short computational time. This research proves that
the PSO algorithm to solve the Vehicle Routing Problem with Time Windows produces a
better solution than the SOS algorithm.
4.6. Implementation of Metaheuristic Method
Based on statistical analysis results, knowing that the PSO algorithm generates bet-
ter objective values with a short computation time than the SOS algorithm. Hence, the
PSO algorithm results to be used do represent the route determination result using me-
taheuristic methods. The results of PSO algorithm implementation on large instance 50
kg and large instance 250 kg data for 7-days delivery are shown in Table 9.
Table 9.Results of PSO Algorithm for 7-Days Delivery
Day Data
Objec-
tive
Route
1
50 10758
26-21-20-19-22-24-23-29-6-5-18-13-14-8-9-30-25-27-28-15-16-1
2-11-10-7-4-3-2-17-1
250 14823
26-25-21-22-19-20-24-23-30-29-3-8-9-15-16-13-17-18-12-11-10-
7-6-5-4-2-27-28-14-1
2
50 10997
1-2-14-16-15-11-29-28-25-30-4-5-3-13-18-17-10-9-19-20-21-22-2
3-24-8-26-27-7-12-6
250 18486
2-26-20-19-24-23-30-9-8-7-13-18-17-16-14-15-25-27-28-21-22-2
9-12-11-10-6-5-4-3-1
34. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 16 of 20
3
50 11348
12-11-26-27-25-2-5-28-29-30-4-14-13-15-9-16-17-18-19-20-21-2
2-23-24-8-7-6-3-10-1
250 17952
4-1-25-19-22-21-20-27-29-3-2-13-14-15-16-17-18-28-26-30-11-1
2-10-9-8-7-23-24-6-5
4
50 11568
4-25-26-20-19-22-23-24-28-30-27-29-2-1-5-10-7-21-15-13-14-16-
17-18-12-11-9-8-6-3
250 21763
7-9-1-2-6-25-19-20-30-10-14-15-16-13-5-28-22-21-24-23-29-18-1
7-8-12-3-26-27-11-4
5
50 12458
2-3-28-22-23-24-25-26-27-29-1-9-12-15-14-19-21-20-30-13-16-1
7-18-11-10-8-7-6-5-4
250 17801
1-7-15-14-13-17-11-12-2-5-6-8-25-26-30-3-16-18-19-20-21-22-23
-24-10-9-27-28-29-4
6
50 11032
28-25-29-21-20-19-2-5-10-27-26-22-24-23-30-7-8-13-14-15-16-1
7-18-9-12-11-6-4-3-1
250 20009
7-9-25-29-3-4-16-14-17-2-1-28-26-27-30-6-13-15-8-10-12-11-18-
19-20-21-22-23-24-5
7
50 11361
27-26-25-29-11-12-2-10-7-9-30-19-22-23-24-13-14-15-16-17-18-
8-28-20-21-6-5-4-3-1
250 19407
2-20-19-27-30-12-13-14-15-16-17-25-28-26-29-6-3-1-10-9-21-22-
23-24-18-7-8-11-5-4
4.7. Comparison Total Cost of Existing and Solution Routes
After obtaining the total cost for each delivery day and vehicle route to be taken, the
next step was to compare the total cost generated by the proposed route versus the ex-
isting transportation cost. The comparison is shown in Table 10.
Table 10.Comparison Total Cost of Existing and Solution Routes
Day
Total Cost
Current
Method
Total Cost Scenario 1 Total Cost Scenario 2
50kg GAP (%) 250kg GAP (%)
1 Rp25.000 Rp10.758 56,97% Rp14.823 40,71%
2 Rp25.000 Rp10.997 56,01% Rp18.486 26,06%
3 Rp25.000 Rp11.348 54,61% Rp17.952 28,19%
4 Rp25.000 Rp11.568 53,73% Rp21.763 12,95%
5 Rp25.000 Rp12.458 50,17% Rp17.801 28,80%
6 Rp25.000 Rp11.032 55,87% Rp20.009 19,96%
7 Rp25.000 Rp11.361 54,56% Rp19.407 22,37%
Based on Table 10, it can be seen that the proposed total cost is lower than the ex-
isting total cost. The gap between the first proposed scenario total cost with the existing
total cost ranges from 50% to 56%. Meanwhile, it ranges from 12% to 40% for the second
proposed scenario total cost compared to the existing total cost. Hence, route determina-
tion in the two proposed scenarios can minimize the transportation cost rather than the
existing method.
35. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 17 of 20
4.8. Investment Feasibility Analysis
The investment feasibility analysis was conducted to discover which scenario, first
or second, that gives profit to the company, whether financial or benefit-wise. In con-
ducting an investment feasibility analysis, the steps conducted are calculating investment
feasibility based on financial analysis and capital budgeting. An analysis of perceived
benefits from the investment plan was also conducted.
4.8.1. Cost Analysis
Cost analysis was conducted to find out the cash flow in a company. There are four
considerations in a company’s financial statements, i.e., investment cost, operational cost,
revenue, and depreciation cost. These four costs are calculated during the vehicle’s eco-
nomic life. The results of cost analysis are a financial statement and net cash flow of the
company when executing the planned investment.
4.8.2. Capital Budgeting Analysis
Capital budgeting was used to determine the acceptance or rejection of an invest-
ment plan to be executed. An investment plan’s feasibility is a consideration in deter-
mining a policy or plan to be carried out. In this research, the capital budgeting methods
used were the net present value (NPV), profitability index (PI), and payback period (PP).
The first and second scenarios calculation results using three capital budgeting methods
are shown in Table 11.
Table 11.Result of Investment Feasibility Analysis
Indicator Criteria
Scenario 1 Scenario 2
Value Decision Value Decision
NPV NPV 0 (Rp 28.299.974)
Not
Feasible
Rp9.149.022 Feasible
Profitability
Index
PI 1 0,739
Not
Feasible
1,112 Feasible
Payback
Period
PP Useful
Life
5 years
Not
Feasible
7,63 years Feasible
Based on Table 11, it is discovered that the first scenario is not feasible to be im-
plemented because the resulting calculation values are not fulfilling all criteria of capital
budgeting calculation methods. In contrast, the second scenario is declared feasible be-
cause the resulting calculation values fulfill all criteria of capital budgeting methods.
4.8.3. Benefit Analysis
A benefit analysis was conducted to discover the company’s perceived benefits by im-
plementing the new distribution system. The perceived benefits are:
1. Saving in distribution costs
By implementing the new distribution method, the company only spent a trans-
portation cost of IDR 18,606. Cost is less than the current transportation cost of the
company for IDR 25,000.
36. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 18 of 20
2. Delivery scheduling
By determining a schedule, the delivery becomes six times per day. It makes the
distribution system more organized and clearer.
3. Optimum operator working time
By implementing the new policy, it will optimize each operator’s working time. The
time can be maximized according to the determined operator’s working time.
4. Product delivery data
With the new policy, delivery is entirely operated by the CK. It will avoid discre-
pancy of inventory in CK.
5. Financial Statement
Different from the current distribution method, this new distribution method has
established the fuel and maintenance costs from the beginning. Thus, the monthly
financial statement will be more organized and clearer.
5. Conclusions
The solution quality resulted from the SOS algorithm has an insignificant difference
with the solution quality PSO algorithm. However, in computation speed to reach the
convergent point, the PSO algorithm has a relatively faster time than the SOS algorithm.
Thus, the PSO algorithm will be implemented on the route determination problem of PT
XYZ. By conducting route determination using metaheuristic approach methods, it saves
daily distribution cost of 56% for the first scenario and 40% for the second scenario. Based
on the feasibility analysis results, the second delivery scenario using three-wheeled mo-
tor vehicles is more feasible to be executed than the first scenario using motor vehicles
with a delivery box. It is proven based on the calculation results using capital budgeting
methods where resulting values fulfill are feasibility criteria in conducting an investment.
Future research may apply and testing SOS and PSO algorithms performance in
another optimization problem, especially in Vehicle Routing Problem (VRP) variations.
Evaluating solution quality and computation times using both algorithms can be sup-
ported by programming skills and better computer specifications. On the other hand, to
get a better solution and computational times, future research may consider other para-
meter values or other parameter tuning methods.
37. J. Open Innov. Technol. Mark. Complex.2021, 7, x FOR PEER REVIEW 19 of 20
6. Patents
This section is not mandatory but may be added if there are patents resulting from
the work reported in this manuscript.
Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1:
title, Table S1: title, Video S1: title.
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their individual contributions must be provided. The following statements should be used “Con-
ceptualization, X.X. and Y.Y.; methodology, X.X.; software, X.X.; validation, X.X., Y.Y. and Z.Z.;
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draft preparation, X.X.; writing—review and editing, X.X.; visualization, X.X.; supervision, X.X.;
project administration, X.X.; funding acquisition, Y.Y. All authors have read and agreed to the
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Authorship must be limited to those who have contributed substantially to the work reported.
Funding: Please add: “This research received no external funding” or “This research was funded
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Appendix A
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to the main text—for example, explanations of experimental details that would disrupt
the flow of the main text but nonetheless remain crucial to understanding and repro-
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References
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tion, Country, 2007; Volume 3, pp. 154–196.
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