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<div class="moz-cite-prefix">On 12/08/2022 11:26, Matthew Knepley wrote:<br>
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<div dir="ltr">On Fri, Aug 12, 2022 at 2:21 AM Quynh Nguyen <<a href="mailto:nguyenquynh9537@gmail.com" moz-do-not-send="true" class="moz-txt-link-freetext">nguyenquynh9537@gmail.com</a>> wrote:<br>
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<div dir="ltr">Dear petsc developers and users,
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<div>I am a new petsc user ^_^.</div>
<div>I have some questions about using DMDA_BOUNDARY_GHOSTED.</div>
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<div>1. I have 2D Poisson code with domain (nx, ny), and I used DMDA_BOUNDARY_NONE, then the size of the matrix is (nx*ny)X(nx*ny).
<b><i>what is the size of the matrix if I used DMDA_BOUNDARY_GHOSTED? is it the same size as DMDA_BOUNDARY_NONE</i></b>?</div>
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<div>Yes, the matrix should be the same size, but local vectors have extra ghost node slots.</div>
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<div>2. if the matrix size of DMDA_BOUNDARY_GHOSTED isn't the same as DMDA_BOUNDARY_NONE,
<b><i>how i can view the matrix including ghost points</i></b>? I ask this one because I used MatView(P, PETSC_VIEWER_STDOUT_WORLD) to show the matrix but excluded ghost points.</div>
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<div>Ghost nodes are there so that stencil operations on local vectors work at boundaries. You fill in the slots with boundary information.</div>
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I can see how this works if you are writing your own solver but can it be used with a KSP? In the case of periodic boundary conditions the boundary values are "filled in" for you by PETSc. Is there any way for a user to supply boundary information to a PETSc
solver when using DMDA_BOUNDARY_GHOSTED?<br>
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Thanks,<br>
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David<br>
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<div> Thanks,</div>
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<div> Matt</div>
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<div>I hope someone can explain my wonder :)</div>
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<div>P/S: maybe, those question is simple and a bit stupid ^_^. </div>
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<div>Have a nice day,</div>
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<div><span style="color:rgb(61,133,198);font-family:"times
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roman",serif;font-size:12.8px">Quynh Nguyen</span><br>
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<div><font face="times new roman,
serif" color="#3d85c6"><span style="font-size:12.8px">Graduate student, Ocean Engineering.</span></font></div>
<div><font face="times new roman,
serif" color="#3d85c6"><span style="font-size:12.8px">School of Naval Architecture and Ocean Engineering, University of Ulsan.</span></font></div>
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<div><font face="times new roman,
serif" color="#3d85c6">-----------------------------------------------------------------------------------------</font></div>
<div><font face="times new roman,
serif" color="#3d85c6">Mobile: (+82) 010-9394-5595 </font></div>
<div><font face="times new roman,
serif" color="#3d85c6">Email:
<a href="mailto:nguyenquynh9537@gmail.com" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">
nguyenquynh9537@gmail.com</a>; <a href="mailto:nguyenthiquynhb_t58@hus.edu.vn" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">
nguyenthiquynhb_t58@hus.edu.vn</a></font></div>
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<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>
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<div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank" moz-do-not-send="true">https://www.cse.buffalo.edu/~knepley/</a><br>
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