Dropping 60 orders of magnitude over 2 orders of magnitude strikes me as a very peculiar definition of linear. It's wikipedia, though, so it must be true.
The sweep convergence of Krisha's plots is second order. The wiki page discusses iterative solvers, which is another layer down from plotting the residual as a function of sweeps. > On Sep 27, 2016, at 7:39 PM, Raymond Smith <[email protected]> wrote: > > I am confused as well now. Comparing with the plots on this Wiki 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 ] > > _______________________________________________ > 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 ]
