I am confused as well now. Comparing with the plots on this Wiki <https://en.wikipedia.org/wiki/Rate_of_convergence> page which are also semi-log, it looks to me like Krishna is seeing linear convergence.
On Tue, Sep 27, 2016 at 3:57 PM, Guyer, Jonathan E. Dr. (Fed) < [email protected]> wrote: > I don't understand what you mean by "supra-linear trend in the semiology > plot". You show clear 2nd order convergence, which is what I would expect. > > > On Sep 27, 2016, at 4:37 PM, Krishna <[email protected]> > wrote: > > > > As you can see, we need supra-linear trend in the semiology plot, such > as to continue with the linear drops achieved in the first few sweeps. > > > > I.e. the solver is effectively bottoming out. Under-relaxation factors, > or solver-changes don't seem to work. > > > > In fact, for certain under-relaxation factors (including 1.0 for 2 of > the variables), it breaks the simulation, and produces NaNs right from the > first sweep. > > > > Krishna > > > > > > > > -------- Original Message -------- > > From: "Gopalakrishnan, Krishnakumar" <[email protected]> > > Sent: Tuesday, September 27, 2016 09:02 PM > > To: [email protected] > > Subject: RE: FiPy sweep convergence bottoms out > > > > Thank you Ray, Thanks for pointing that out. > > > > > > > > Here’s the link to Semilog plot. It takes nearly 22 sweeps to achieve a > tolerance of 10^-4 for \phi_e and \phi_s_neg. > > > > > > > > Furthermore, the time spent in sweeping (within each time-step) > increases as time progresses. > > > > > > > > https://imperialcollegelondon.box.com/s/4ix6pozs1h9syt1r3fbkw2pi05ooicmy > > > > > > > > Krishna > > > > > > > > From: [email protected] [mailto:[email protected]] On Behalf Of > Raymond Smith > > Sent: Tuesday, September 27, 2016 8:51 PM > > To: [email protected] > > Subject: Re: FiPy sweep convergence bottoms out > > > > > > > > Hi, Krishna. > > > > It would be more clear to plot the residuals on a semi-log plot (or > equivalently plot the log of residual vs sweep number) to more clearly show > the value of the small residuals, as the plots in that link make it look to > me like the residuals all go to zero. > > > > Ray > > > > > > > > On Tue, Sep 27, 2016 at 12:42 PM, Gopalakrishnan, Krishnakumar < > [email protected]> wrote: > > > > > > > > Hi, > > > > > > > > We are solving a system of 5 coupled non-linear PDEs. > > > > > > > > As shown in this plot of residuals vs. sweep count > https://imperialcollegelondon.box.com/s/9davbq2gq5eani98xuuj2cw9tmz4mbu3 > , our residuals die down very slowly, i.e. the solver bottoms out. The > drop in all the residuals is linear at first, and then asymptotically > bottoms out to a value. > > > > > > > > How do we get our residuals to drop faster, i.e. with lesser sweeps and > faster convergence ? I tried changing solvers and tolerances, but curiously > enough the results remain identical. > > > > > > > > Any pointers on this will be much appreciated. > > > > > > > > > > > > Krishna > > > > > > > > > > > > > > > > > > _______________________________________________ > > fipy mailing list > > [email protected] > > http://www.ctcms.nist.gov/fipy > > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > > > > > > > _______________________________________________ > > fipy mailing list > > [email protected] > > http://www.ctcms.nist.gov/fipy > > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > > _______________________________________________ > fipy mailing list > [email protected] > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] >
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