It is known that the conventional algorithm (CA) of hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) usually suffers the problem of slow convergence, and the decomposition algorithm (DA) is limited by large memory requirement. An efficient twofold iterative algorithm (TIA) of FE-BI-MLFMA is presented using the multilevel inverse-based incomplete LU (MIB-ILU) preconditioning in this paper. It is shown that this TIA can offer a good balance of efficiency between CPU time and memory requirement. The tree-cotree splitting technique is then employed in the TIA to further improve its efficiency and robustness. A variety of numerical experiments are performed in this paper, demonstrating that the TIA exhibits superior efficiency in memory and CPU time to DA and CA, and greatly improves the computing capability of FE-BI-MLFMA.
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