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p-refinementincrease the order of interpolation polynomialsGavrilovic et al., IEEE Trans. Magn., 33 (1997) 4128.
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r-refinementreduce element size by moving nodesnumber of unknowns remains constant
 Hertel et al., IEEE Trans. Magn. 34 (1998) 3922.
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h-refinementadditional degrees of freedom by inserting nodes and elementsHertel et al., IEEE Trans. Magn. 34 (1998) 3922.
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h-refinementadditional degrees of freedom by inserting nodes and elementsBagnérés-Viallix et al., IEEE Trans. Magn., 27 (1991) 3819
 Tako et al., J. Appl. Phys. 81 (1997) 4082
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