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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Dear Xavier,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Physical groups are explained in
<a href="http://gmsh.info/doc/texinfo/gmsh.html#Elementary-entities-vs-physical-groups">
Section 6.2 of Gmsh manual</a>. The TL;DR is: when some part of the mesh (a node, edge, face or element) is part of a physical group, it is marked with a numerical “tag”. Constituents of the mesh can receive more than one “tag” when they belong to the intersection
of different physical groups. The solver using the mesh then reconstructs the physical groups by looking for element carrying a certain tag.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">As for the formatting of the .msh file, it is explained in
<a href="http://gmsh.info/doc/texinfo/gmsh.html#MSH-file-format">Section 9.1 of the documentation</a>. The .msh file has a $Entities section in which you will find the mesh constituents (nodes, edges, faces and volumes) and each will be marked with the physical
“tags” you defined in your .geo file.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Sincerely Yours,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Guillaume Dilasser<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">De :</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> gmsh <gmsh-bounces@ace20.montefiore.ulg.ac.be>
<b>De la part de</b> Xavier Johnson<br>
<b>Envoyé :</b> vendredi 21 février 2020 02:58<br>
<b>À :</b> gmsh@onelab.info<br>
<b>Objet :</b> [Gmsh] Clarification on Element Physical Group Relation<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hello,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I had some confusion when I assign a physical group in the gmsh program to how those physical groups relate to the generated mesh elements. This is more of a concern when I am trying to get an understanding on the information about the
elements in the output .msh file. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Any clarification would be useful.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thank you,<o:p></o:p></p>
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<p class="MsoNormal">Xavier <o:p></o:p></p>
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