<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""></div> For TSBEULER (the theta method) see <a href="https://petsc.org/release/docs/manualpages/TS/TSTHETA.html" class="">https://petsc.org/release/docs/manualpages/TS/TSTHETA.html</a> and look at the source code src/ts/impls/implicit/theta/teta.c for TSStep_Theta. You can use -snes_monitor_solution OPTIONS to see what the solutions are the nonlinear system look like as it solves the system.<div class=""><br class=""></div><div class=""><br class=""><div class=""><br class=""></div><div class=""> Barry</div><div class=""><br class=""></div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Oct 11, 2021, at 12:26 PM, Alfredo J Duarte Gomez <<a href="mailto:aduarteg@utexas.edu" class="">aduarteg@utexas.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="">Good morning PETSC team,</div><div class=""><br class=""></div><div class="">I have a working algorithm for my implicit TS integrator with a system of ODE/DAE's, but I am observing a rather high number of iterations<br class=""></div><div class=""><br class=""></div><div class="">I am currently using the simplest settings of a TSBEULER and setting a constant time step.</div><div class=""><br class=""></div><div class="">My question right now is whether the default settings use any sort of initial guess algorithm before every time step. <br class=""></div><div class=""><br class=""></div><div class="">Since I have seen that the time step adapter calculates the Local Truncation Error, it should be possible to use an extrapolation of arbitrary order of accuracy as an initial guess for every time step right? Can someone indicate how I would be able to use that?</div><div class=""><br class=""></div><div class="">Additionally, it would be very helpful to take a look at that initial guess, is it possible to use any existing function to calculate it either in the PreStep or PostStep function to visualize it?</div><div class=""><br class=""></div><div class="">Thank you,</div><br class="">-- <br class=""><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><font face="arial, sans-serif" class="">Alfredo Duarte</font><div class=""><font face="arial, sans-serif" class="">Graduate Research Assistant</font></div><div class=""><font face="arial, sans-serif" class="">The University of Texas at Austin</font></div></div></div></div></div></div>
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