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<p class="MsoNormal"><span style="font-size:11.0pt">Hi Bowen,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">We don’t always include descriptions of unit tests in the guide, because these are intended to test specific parts of the code rather than provide users with example setups. The MagDiff test you mentioned
is a simple Gaussian diffusion of B-field, which has an analytic solution when the diffusivity is constant.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">When you switch to the ‘explicit’ solver, you have to keep a couple of things in mind. The explicit solver is in the Hydro unit, so you need useHydro and updateHydroFluxes to be true. You will also need to
be limiting your timestep dt by the magnetic diffusion time, so you need useDiffuseComputeDtMagnetic = .true. and dt_diff_factor should be set to a value <= 1.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black">--</span><span style="font-size:10.0pt;font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#181A1B">Eddie Hansen</span><span style="font-size:10.0pt;font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#181A1B">Applications Group Leader<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#181A1B">Flash Center for Computational Science</span><span style="font-size:10.0pt;font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="color:black">From:
</span></b><span style="color:black">flash-users <flash-users-bounces@flash.rochester.edu> on behalf of Bowen Zhu (Student at CentraleSupelec) <bowen.zhu@student-cs.fr><br>
<b>Date: </b>Saturday, March 23, 2024 at 3:18 PM<br>
<b>To: </b>flash-users@flash.rochester.edu <flash-users@flash.rochester.edu><br>
<b>Subject: </b>[FLASH-USERS] Switching Magnetic Diffusion Solvers in Zpinch Simulations<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Dear Community,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">I'm currently exploring Z-pinch simulations in FLASH, focusing on comparing the explicit and implicit magnetic diffusion solvers. While I aim to validate computation results and address concerns about potential
bugs in the implicit solver, I've encountered challenges in switching from the implicit to the explicit solver. Changing resistivitySolver from "implicit" to "explicit" doesn't seem to activate the explicit solver effectively; the simulation results mimic
those without applying magnetic resistivity (useMagneticResistivity = .false.), where the plasma remains static.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">As someone new to FLASH, I wonder if there are additional steps required to successfully switch to the explicit solver.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Furthermore, in my efforts to validate the solvers' differences, I discovered an example under /magnetoHD/unitTest/MagDiff that seems to implement both solvers. However, I found no description of this example in
the user manual or user archives. Could anyone provide insights into the problem this example addresses and any available analytical solutions for reference?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Your guidance on these matters would be immensely appreciated.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Bon weekend,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Best regards,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Bowen ZHU<o:p></o:p></span></p>
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