# solver tolerance in fvSolution

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 March 21, 2011, 08:31 solver tolerance in fvSolution #1 Member   fisch Join Date: Feb 2010 Posts: 97 Rep Power: 9 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

 March 22, 2011, 09:22 #2 Senior Member   BastiL Join Date: Mar 2009 Posts: 502 Rep Power: 13 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 kiddmax, vetri, vishwakarma and 8 others like this.

 March 22, 2011, 09:43 #3 Member   fisch Join Date: Feb 2010 Posts: 97 Rep Power: 9 Thanks for the reply Bastian, but the question is still how the (total) residuum is calculated or what it means.. Do you know that?

 March 22, 2011, 14:43 #4 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,910 Rep Power: 28 Please check here: http://www.cfd-online.com/Forums/ope...d-solvers.html Google knows ;-) fumiya and Pirlu like this. __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 March 23, 2011, 02:35 #5 Member   fisch Join Date: Feb 2010 Posts: 97 Rep Power: 9 thank you alberto

August 15, 2016, 03:28
tolerance relTol question
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amin jalalian
Join Date: Mar 2014
Posts: 34
Rep Power: 5
Quote:
 Originally Posted by bastil 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

1- O.F uses relTol or tolerance for stop iteration?
2- What is difference between tolerance in for example "U" and "UFinal"?

Thanks.

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