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 fisch March 21, 2011 08:31

solver tolerance in fvSolution

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:confused:. 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

 bastil March 22, 2011 09:22

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

 fisch March 22, 2011 09:43

but the question is still how the (total) residuum is calculated or what it means..
Do you know that?

 alberto March 22, 2011 14:43

 fisch March 23, 2011 02:35

thank you alberto

 amin_jalalian August 15, 2016 03:28

tolerance relTol question

Quote:
 Originally Posted by bastil (Post 300525) 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