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solver tolerance in fvSolution

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Old   March 21, 2011, 08:31
Default solver tolerance in fvSolution
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fisch
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Hello,

i found a lot of posts in the forum where some solver tolerances within openFOAM are suggested as accurate. For example in the fvSolution file for solving the p-equation is "tolerance 1e-6", "1e-4" or "1e-8".
I wanted to figure out how this tolerance number is calculated to estimate a number for my simulations, but i can't get it out of the code. Is there any explanation what this residual number / norm means or which norm is taken from the residual vector!?

A little example would be very nice (for example in relative error if i would have only one cell ... or something else)

Thanks a lot.
rupert
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Old   March 22, 2011, 09:22
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Well,

the relTol is the relative tolerance between the initial and the final residual. Both are reported by the solver:
GAMG: Solving for p, Initial residual = 0.0334352, Final residual = 0.000941545, No Iterations 17

if you specify a relTol of 0.1 the solver will stop iterating if the final residual falls below 0.1*0.0334352=0.00334352.
The absolute tolerance you refer to with "tolerance" in fvSolution is the value the Final residual need to fall below.

Regards Bastian
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Old   March 22, 2011, 09:43
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Thanks for the reply Bastian,

but the question is still how the (total) residuum is calculated or what it means..
Do you know that?
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Old   March 22, 2011, 14:43
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Alberto Passalacqua
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Please check here: Residuals for convergence of segregated solvers

Google knows ;-)
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Old   March 23, 2011, 02:35
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thank you alberto
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