<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Apr 6, 2020 at 3:47 PM Jed Brown <<a href="mailto:jed@jedbrown.org">jed@jedbrown.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">This typically happens when your model is discontinuous or you activate<br>
some fast transitien. You have a really aggressive lower bound on your<br>
time step so its hard to tell here.<br></blockquote><div><br></div><div>The time step goes down to like 1e-3. </div><div>I am suspecting that my source term needs to be smoother and am working on that now.</div><div>It is disconcerting that the truncation error goes up as the time stp is reduced, but in this example it does start to go down again.</div><div>Thanks,</div><div>Mark</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
Mark Adams <<a href="mailto:mfadams@lbl.gov" target="_blank">mfadams@lbl.gov</a>> writes:<br>
<br>
> I have a problem that is fairly smooth and when it decreases the time step<br>
> it just keeps decreasing almost forever. I wanted to see if anyone has any<br>
> clue what is going on here.<br>
><br>
> This test reaches a quasi equilibrium and the adaptivity uses fairly large<br>
> time steps with dU/dt - F(u,t) = 0. I set a max time step of 10. A source<br>
> starts at one point (dU/dt - F(u,t) = S(t)). It cools pretty fast.<br>
><br>
> THe truncation error increase a lot when the source starts but it does not<br>
> decrease the time step immediately because I had a mat time step set:<br>
> ....<br>
> Nonlinear solve converged due to CONVERGED_FNORM_RELATIVE iterations 4<br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local *truncation error<br>
> 0.000214757*, accepting step of size 10.<br>
> TSAdapt basic arkimex 0:1bee step *386* accepted t=2292.68 +<br>
> 1.000e+01 dt=1.000e+01 wlte=0.000215 wltea= -1 wlter= -1<br>
> ...<br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local *truncation error<br>
> 0.500399,* accepting step of size 10.<br>
> TSAdapt basic arkimex 0:1bee step *387* accepted t=2302.68 +<br>
> 1.000e+01 dt=1.000e+01 wlte= 0.5 wltea= -1 wlter= -1<br>
> 388) species-0: charge density= -1.6422881272166e+01 z-momentum=<br>
> 7.2180929658011e-03 energy= 9.7881753794625e+05<br>
><br>
> It goes for another few time steps before it rejects the time step for the<br>
> first time, and then it just keeps reducing and reducing:<br>
><br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error<br>
> 0.939966, accepting step of size 10.<br>
> TSAdapt basic arkimex 0:1bee step *395* accepted t=2382.68 +<br>
> 1.000e+01 dt=9.283e+00 wlte= 0.94 wltea= -1 wlter= -1<br>
> ....<br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error 1.33533,<br>
> *rejecting* step of size 9.28296<br>
> TSAdapt basic arkimex 0:1bee step *396* rejected t=2392.68 +<br>
> 9.283e+00 dt=7.230e+00 wlte= 1.34 wltea= -1 wlter= -1<br>
><br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error 1.44054,<br>
> *rejecting* step of size 7.22994<br>
> TSAdapt basic arkimex 0:1bee step *396* rejected t=2392.68 +<br>
> 7.230e+00 dt=2.711e+00 wlte= 1.44 wltea= -1 wlter= -1<br>
><br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error 1.63529,<br>
> *rejecting* step of size 2.71072<br>
> TSAdapt basic arkimex 0:1bee step *396* rejected t=2392.68 +<br>
> 2.711e+00 dt=9.539e-01 wlte= 1.64 wltea= -1 wlter= -1<br>
><br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error 1.60415,<br>
> *rejecting* step of size 0.953894<br>
> TSAdapt basic arkimex 0:1bee step *396* rejected t=2392.68 +<br>
> 9.539e-01 dt=5.000e-01 wlte= 1.6 wltea= -1 wlter= -1<br>
><br>
> [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error<br>
> 1.49714, *accepting<br>
> because step size 0.5 is at minimum*<br>
> TSAdapt basic arkimex 0:1bee step *396* accepted t=2392.68 +<br>
> 5.000e-01 dt=5.000e-01 wlte= 1.5 wltea= -1 wlter= -1<br>
><br>
> Anyone have any idea what is going on here?<br>
><br>
> Thanks,<br>
> Mark<br>
</blockquote></div></div>