<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Aug 17, 2017 at 3:13 AM, Maximilian Hartig <span dir="ltr"><<a href="mailto:imilian.hartig@gmail.com" target="_blank">imilian.hartig@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word">Thanks for your help Matt.<br><div><blockquote type="cite"><div>On 16. Aug 2017, at 16:17, Matthew Knepley <<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>> wrote:</div><br class="gmail-m_-3501194453730676254Apple-interchange-newline"><div><div dir="ltr" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div class="gmail_extra"><div class="gmail_quote">On Wed, Aug 16, 2017 at 8:56 AM, Maximilian Hartig<span class="gmail-m_-3501194453730676254Apple-converted-space"> </span><span dir="ltr"><<a href="mailto:imilian.hartig@gmail.com" target="_blank">imilian.hartig@gmail.<wbr>com</a>></span><span class="gmail-m_-3501194453730676254Apple-converted-space"> </span>wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello,<br><br>I have a problem with several fields that I solve with PetscFE and TS. I now need to access the solution from the previous timestep to compute the residual for the current timestep.<br>I tried a TSMonitor with the following code in it:<br><br>TSGetDM(ts,&dm);<br>DMClone(dm,&dm_aux);<br>DMGetDS(dm,&prob_aux);<br>DMSetDS(dm_aux,prob_aux);<br>DMCreateGlobalVector(dm_aux,&o<wbr>ld_solution);<br>VecCopy(u,oldsolution);<br>PetscObjectCompose((PetscObjec<wbr>t) dm, “A”, (PetscObject) old_solution);<br><br>VecDestroy(&old_solution);<br>DMDestroy(&dm_aux);<br><br>hoping that it would create an auxiliary field that I could access in the evaluation of the residual. It did that but messed with the discretisation of the initial problem in some way. So I figure that adding auxiliary fields to a dm after having fed it to a TS context is not something you should be doing.<br><br>Is there a way to access the fields of the solution for the previous timestep during the evaluation of the current residual?<br></blockquote><div><br></div><div>First, I can show you how to do what you are asking for. I think you can simply</div><div><br></div><div>PetscObjectQuery((PetscObject) dm, "old_solution", (PetscObject *) &old_solution);</div><div>if (!old_solution) {</div><div> DMCreateGlobalVector(dm, &old_solution);</div><div> PetscObjectCompose((<wbr>PetscObject) dm, "old_solution", old_solution);</div><div>}</div><div>VecCopy(u, oldsolution);</div></div></div></div></div></blockquote><br><div>Unfortunately, this produces an error and tells me “An object cannot be composed with an object that was composed with it."</div><br><blockquote type="cite"><div><div dir="ltr" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div class="gmail_extra"><div class="gmail_quote"><div><br></div><div>Second, I think a better way to do this than composition is to use</div><div><br></div><div> DMGetNamedGlobalVector(dm, "old_solution", &old_solution);</div></div></div></div></div></blockquote><div><br></div><div>Yes, this seems to work and I do not get an error while running the monitor. Also the discretisation seems to be fine. But the old solution now is not available as an auxiliary field.</div><br><blockquote type="cite"><div><div dir="ltr" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div class="gmail_extra"><div class="gmail_quote"><div><br></div><div>Third, I can say that I am profoundly troubled by this. This interferes with the operation of</div><div>the time integrator, and I cannot see a reason for this. If you are keeping track of the integral</div><div>of some quantity, I would update that in TSPostStep() and request that integral instead of the</div><div>previous solution. We do this for some non-Newtonian rheologies.</div></div></div></div></div></blockquote><div><br></div><div>I have an “if” condition in my residual which I need to evaluate to determine the correct formulation for my residuals. I use actual fields to keep track of the integrals. But when I use the actual field to evaluate the “if” condition, due to the implicit nature of the solver I jump “back and forth” over that condition. I need the “if” condition to be independent from the field for which it determines the residual.</div><div>The actual application is as follows:</div><div> I have, amongst others, a displacement and a stress field.</div><div>I evaluate for my stress given a displacement increment delta u.</div><div>If the resulting stress is > yield stress, I need a plasticity formulation, if it is smaller, I can use elasticity.</div></div></div></blockquote><div><br></div><div>Hmm, I think this is a formulation problem. You should be using the "correct" formulation at the implicit step, since otherwise</div><div>the residual will be inconsistent with what you tested when evaluated at the new step. I have the same kind of elasto-plastic</div><div>system in PyLith (<a href="http://www.geodynamics.org/cig/software/pylith/">http://www.geodynamics.org/cig/software/pylith/</a>) which we solve implicitly without much problem.</div><div><br></div><div> Thanks,</div><div><br></div><div> Matt</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"><div style="word-wrap:break-word"><div><div>Thanks,</div><div>Max</div><div><br></div><blockquote type="cite"><div><div dir="ltr" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div class="gmail_extra"><div class="gmail_quote"><div><br></div><div> <span class="gmail-m_-3501194453730676254Apple-converted-space"> </span>Thanks,</div><div><br></div><div> Matt</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">Thanks,<br>Max</blockquote></div><br><br clear="all"><span class="gmail-HOEnZb"><font color="#888888"><div><br></div>--<span class="gmail-m_-3501194453730676254Apple-converted-space"> </span><br><div class="gmail-m_-3501194453730676254gmail_signature"><div dir="ltr"><div>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener</div><div><br></div><div><a href="http://www.caam.rice.edu/~mk51/" target="_blank">http://www.caam.rice.edu/~<wbr>mk51/</a></div></div></div></font></span></div></div></div></blockquote></div><br></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><div>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener</div><div><br></div><div><a href="http://www.caam.rice.edu/~mk51/" target="_blank">http://www.caam.rice.edu/~mk51/</a><br></div></div></div>
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