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<br><br><div class="gmail_quote">On Tue, Oct 22, 2013 at 5:36 PM, Christophe Ortiz <span dir="ltr"><<a href="mailto:christophe.ortiz@ciemat.es" target="_blank">christophe.ortiz@ciemat.es</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote"><div>On Tue, Oct 22, 2013 at 3:37 PM, Matthew Knepley <span dir="ltr"><<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div>On Tue, Oct 22, 2013 at 8:29 AM, Christophe Ortiz <span dir="ltr"><<a href="mailto:christophe.ortiz@ciemat.es" target="_blank">christophe.ortiz@ciemat.es</a>></span> wrote:<br>
</div><div class="gmail_extra">
<div class="gmail_quote"><div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">Hi Barry,<div>
<br></div><div>Thanks for suggestions. Here is the output.</div><div>
Before using the options you suggest I get:</div><div><br></div><div><div> TSAdapt 'basic': step 182 accepted t=0.341561 + 3.416e-02 wlte=1.1e-09 family='arkimex' scheme=0:'3' dt=3.757e-02 </div>
<div> TSAdapt 'basic': step 183 accepted t=0.375717 + 3.757e-02 wlte=9.05e-14 family='arkimex' scheme=0:'3' dt=4.133e-02 </div><div> TSAdapt 'basic': step 184 stage rejected t=0.413289 + 4.133e-02 retrying with dt=1.033e-02 </div>
<div> TSAdapt 'basic': step 184 stage rejected t=0.413289 + 1.033e-02 retrying with dt=2.583e-03 </div></div><div>...</div><div><div> TSAdapt 'basic': step 184 stage rejected t=0.413289 +2.212e-198 retrying with dt=5.529e-199</div>
<div> TSAdapt 'basic': step 184 stage rejected t=0.413289 +5.529e-199 retrying with dt=1.382e-199</div><div>[0]PETSC ERROR: --------------------- Error Message ------------------------------------</div><div>
[0]PETSC ERROR: Floating point exception!</div><div>[0]PETSC ERROR: Vec entry at local location 12 is not-a-number or infinite at end of function: Parameter number 3!</div></div><div><br></div><div><br></div><div> I re-checked my Jacobian several times, and I found few errors. But now I think it is ok.<br>
</div><div>Then, with the options you suggest, it stops immediatly. Not even one timestep:</div></div></blockquote><div><br></div></div><div>Something is very wrong here. The Jacobian should at least have something on the diagonal from the time derivative,</div>
<div>but the Laplacian (u, v) and q (w) also have diagonals.</div><div><br></div><div> Matt</div><div><br></div></div></div></div></blockquote></div></div></div></div></blockquote><div><br></div><div>Hi guys,</div><div>
<br></div><div>I finally found what was wrong. I used -mat_view to check each element of the Jacobian. The structure was ok but there was some unexpected values. Then I checked my code and found a mistake while assigning values to some array (the diagonal block). It was cumulating values during the loop for (row i) {}. Now, at the beginning of the loop I use PetscMemzero(array) to reset the array.</div>
<div><br></div>
<div>Now it works much better with 1bee and linesearch bt. It converges quickly to large times in few timesteps.</div><div>Thanks all for your help and sorry to bother you so much :-).</div><div><br></div><div>Nevertheless...I still observe some problem, some oscillations in the solution, but in some extreme cases. It occurs with the following system, when q is very large:</div>
<div><br></div><div>u_t - alpha u_xx + (k.u.v - q.w) = 0</div><div>v_t - alpha v_xx + (k.u.v - q.w) = 0<br></div><div>w_t - (k.u.v - q.w) = 0<br></div><div><br></div><div>I guess the problem becomes stiff.</div><div>I tried assuming that the reaction is in steady state (w_t=0) and modifying the IJacobian accordingly, but it did not work.</div>
<div><br></div><div> Any suggestion to circumvent that ?<br></div><div>Christophe</div><div><br></div><div><br></div></div></div>
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