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Forgive me if my question is simple and please feel free to refer to an old answer. I am experimenting with preconditioned GMRes with no restart. I wonder if there is an interpretation of this plateau in the GMRes residual plot? I mean that the convergence curve shows several distinct intervals with different slopes and almost stalled after the 500th iteration, but eventually begin to reduce residual again.

Thank you.

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lumberman
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  • I’d be curious what happens after iteration 1000. With residuals that small, you’re starting to near the point where it’s hard for an iterative method to drive the residual norm any lower due to floating point issues. – eepperly16 May 25 '21 at 02:06

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