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Number of iteration difference between PCG and GAMG

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Old   November 22, 2022, 06:52
Default Number of iteration difference between PCG and GAMG
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I ran two interFOAM multiphase simulation in which one had the p_rgh solver set as PCG and one in which it was GAMG. The preconditioner for both was set to DIC. I observed that the number of iterations taken to converge to 1e-8 is higher for PCG (about 1000) and lower for GAMG (about 40). Why does this occur ?
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Old   November 22, 2022, 07:36
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Domenico Lahaye
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GAMG requires less iterations because it iterates on various levels of accuracy. See literature on Multigrid Methods, e.g., book of Moukalled-Darwish-Mangani or https://en.wikipedia.org/wiki/Multigrid_method.

I suggest using GAMG as preconditioner for CG to combine best of two worlds (zat least in case that number of processors is one or small).
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