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<p>Hi Nicolas,</p>
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<p>You can use gradm1 to get your strong divergence.</p>
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<p>Laplacian is a bit trickier since the 2nd derivative really is well-defined.</p>
<p>Some people compute the gradient and then apply dsavg() to each component</p>
<p>prior to taking the divergence of that field.</p>
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<p>Right now there are no tools to do exactly the thing you want, so using gradm1()</p>
<p>is as good as any option.</p>
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<p>Note that gradm1() is as efficient (or more so) than some of the other tools</p>
<p>to compute gradient in Nek. In order to get (say) du/dx, you have to compute</p>
<p>du/dr , du/ds , du/dt, and then get du/dx from the chain rule. du/dy, du/dz</p>
<p>also come from the chain rule, almost for free, even though you don't need them.</p>
<p>So you can simplify everything just through repeated use of gradm1.</p>
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<p>Best, Paul</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Nek5000-users <nek5000-users-bounces@lists.mcs.anl.gov> on behalf of nek5000-users@lists.mcs.anl.gov <nek5000-users@lists.mcs.anl.gov><br>
<b>Sent:</b> Tuesday, October 3, 2017 12:12:59 PM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> [Nek5000-users] Strong divergence and Laplacian operator</font>
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<div>Hi all,<br>
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I need to compute some operators in the strong form directly for a project, i.e. without the mass matrix included in the operator.<br>
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For the convection and gradient operators, I am using the functions convop and gradm1 respectively. However, I would also need to compute strong divergence and Laplacian and I did not find the corresponding functions (opdiv and axhelm are computing the weak
form if I understand correctly). Do such functions exist? Or what modifications should I bring to the existing routines to change them to strong form?<br>
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Best regards,<br>
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Nicolas<br>
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