## 3 Research Methodology
### Category Classification  
Table 4 presents the classification of the SMP. The classification is categorised into five different categories. The first category is the problem types. Then, it is followed by  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Type of Publication**} & \multicolumn{10}{c}{**Year**} \\ \cline{2-13}  & **2010** & **2011** & **2012** & **2013** & **2014** & **2015** & **2016** & **2017** & **2018** & **2019** & **2020** & **2021** & **Total** \\ \hline Journal & 0 & 4 & 3 & 5 & 6 & 7 & 9 & 10 & 12 & 13 & 15 & 3 & 87 \\ Conference Proceedings & 0 & 4 & 5 & 2 & 2 & 3 & 2 & 3 & 1 & 1 & 0 & 0 & 23 \\ \hline Total & 0 & 8 & 8 & 7 & 8 & 10 & 11 & 13 & 13 & 14 & 15 & 3 & 110 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Distribution of papers according to type of publication over the years.  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Country**} & \multicolumn{10}{c}{**Year**} \\ \cline{2-13}  & **2010** & **2011** & **2012** & **2013** & **2014** & **2015** & **2016** & **2017** & **2018** & **2019** & **2020** & **2021** & **Total** \\ \hline USA & 0 & 1 & 3 & 1 & 4 & 1 & 2 & 5 & 5 & 3 & 5 & 1 & 31 \\ Ireland & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 \\ Norway & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 1 \\ Turkey & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 1 \\ France & 0 & 0 & 0 & 2 & 0 & 3 & 1 & 1 & 0 & 0 & 1 & 0 & 8 \\ Italy & 0 & 0 & 0 & 1 & 0 & 1 & 1 & 1 & 0 & 0 & 0 & 0 & 4 \\ Taiwan & 0 & 3 & 1 & 0 & 2 & 0 & 1 & 0 & 1 & 1 & 1 & 0 & 10 \\ Singapore & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 1 & 0 & 0 & 2 \\ Austria & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 1 \\ China & 0 & 0 & 0 & 0 & 2 & 2 & 1 & 0 & 2 & 3 & 0 & 10 \\ Switzerland & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 1 \\ Korea & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0 & 1 \\ Brazil & 0 & 0 & 1 & 0 & 1 & 0 & 0 & 0 & 0 & 0 & 2 \\ Luxembourg & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 1 \\ Australia & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 1 \\ Iran & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 1 \\ \hline Total & 0 & 4 & 4 & 5 & 7 & 9 & 8 & 10 & 7 & 8 & 13 & 1 & 76 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Distribution of Papers according to Real-World Dataset over the Years.  
Figure 2: Numbers of Papers based on the Year of Publication.  
the problem variants category. There are two different categories in terms of the problem variants. The first problem variant is based on the number of drivers and riders (D-R) while the second problem variant is based on the number of origins and destinations (O-D). It was the authors of [5] who proposed a ridesharing classification based on the number of D-R involved. For this variant, there are four different sub-categories, which are One-to-One (1-1), One-to-Many (1-M), Many-to-One (M-1), and Many-to-Many (M-M). They represent a single driver-single rider, single driver-multiple riders, multiple driver-single rider, and multiple driver-multiple riders, respectively. Ref. [15] concentrated on carpooling problem variant and proposed that the second problem variant which can also be divided into four sub-categories. They are One Origin-One Destination (IO1D), One Origin-Multiple Destinations (1 OMD), Multiple Origins-One Destination (MO1D), and Multiple Origins-Multiple Destinations (MOMD). The third category is classified based on data characteristics. The data characteristics are static, stochastic, and dynamic. The fourth and last category is based on solution approaches. The solution approaches consist of exact, heuristic and metaheuristics, and other algorithms.