Very small residual
Hi everyone!
For common residual definition which is, r = b  A*y I get a very small value even at the beginning (about e5). So I'm not sure how I can set a criterion of convergence. Waiting your precious answers. 
One option could be using normalized value for setting convergence criterion;
Rn_i=R_i/R_1 < tolerance where, Rn_i= normalized residual from the ith iteration R_i = residual from the ith iteration R_1= residual from the 1st iteration (generally max residual) 
Mr. Ertan
Thank you. But in this case what should be the proper tolerance? How can I be sure that, chosen tolerance is enough for accurate results? 
Quote:

That depends on how much accuracy you need. For unsteady flows, it should be safe to can pick a tolerance (convergence criterion) of 0.001 or less for the normalized residuals. For steady flows, I would suggest setting the convergence criterion to a very low value, such as 10^10. This way you could minimize the iteration error in your calculations. (If you plot residuals, you should be able to see them level off (flatten) after a while).
HTH 
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