## 3 Parallel Computing Based on a Hybrid OpenMP-MPI Approach
### Parallelization Strategy Based on Hybrid OpenMP-MPI Approach
The proposed approach has a potential great impact on the efficient use of parallel computational resources, suggesting an efficient handling of tasks and threads, to avoid resources (cores and/or ram) being idle while the other processes are running elsewhere. Conceptualization, S.V. ; methodology, A.C., A.M., G.G., F.C. and S.V. ; software and validation, F.C. and S.V. ; writing, A.C. and A.M.; supervision, F.V. All authors have read and agreed to the published version of the manuscript. The work was partially supported by the Projects: \"Smart Distributed Systems\" under the program \"Dipartimenti di Eccellenza 2018-2022\", and the program PRIN, grant # 20177 BZMAH, funded by MIUR, Italian Ministry of University and Research, and by the project \"LargeEM\", 3 rd Marconi Fusion cycle. The authors declare no conflict of interest. ## References

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\begin{tabular}{c c c} \hline \hline
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22 (reference) & 1 (reference) & 1.0 \\
22 & 25 & 23.9 \\
22 & 36 & 33.1 \\
22 & 64 & 53.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Case study 2: speed-up values for task b, with OpenMP–MPI on MARCONI Cluster. \begin{table}
\begin{tabular}{c c c} \hline \hline
**OpenMP Threads per Node** & **Nodes 2 MPI per Node** & **Speed-Up** \\ \hline
22 (reference) & 2 (reference) & 1.0 \\
11 & 8 & 2.4 \\
22 & 8 & 4.3 \\
11 & 18 & 4.9 \\
22 & 18 & 7.9 \\ \hline \hline \end{tabular}
\end{table} 
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