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<div dir="ltr" class="gmail_attr">On Sat, Jul 20, 2019 at 5:47 AM José Lorenzo via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<br>
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<div>Hello,</div>
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<div>I am not sure I understand the function VecGhostRestoreLocalForm. If I proceed as stated in the manual,<br>
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<pre> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecGhostUpdateBegin.html#VecGhostUpdateBegin" target="_blank">VecGhostUpdateBegin</a>(x,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/INSERT_VALUES.html#INSERT_VALUES" target="_blank">INSERT_VALUES</a>,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/SCATTER_FORWARD.html#SCATTER_FORWARD" target="_blank">SCATTER_FORWARD</a>);
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<pre> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecGhostUpdateEnd.html#VecGhostUpdateEnd" target="_blank">VecGhostUpdateEnd</a>(x,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/INSERT_VALUES.html#INSERT_VALUES" target="_blank">INSERT_VALUES</a>,<a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/SCATTER_FORWARD.html#SCATTER_FORWARD" target="_blank">SCATTER_FORWARD</a>);
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<pre> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecGhostGetLocalForm.html#VecGhostGetLocalForm" target="_blank">VecGhostGetLocalForm</a>(x,&xlocal);
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<pre> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecGetArray.html#VecGetArray" target="_blank">VecGetArray</a>(xlocal,&xvalues);
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<pre> // access the non-ghost values in locations xvalues[0:n-1] and ghost values in locations xvalues[n:n+nghost];
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<pre> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecRestoreArray.html#VecRestoreArray" target="_blank">VecRestoreArray</a>(xlocal,&xvalues);
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<pre> <a href="https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecGhostRestoreLocalForm.html#VecGhostRestoreLocalForm" target="_blank">VecGhostRestoreLocalForm</a>(x,&xlocal)<br><br></pre>
<pre>Does VecRestoreArray update the values in the local vector xlocal, and then VecGhostRestoreLocalForm update the values of the global vector x? <br></pre>
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<div>Yes, you can think VecRestoreArray finalizes the updates to xlocal. VecGhostRestoreLocalForm does not update global vector. It is for bookkeeping purposes.</div>
x and xlocal share the same memory that contains the actual vector data. If you changed ghost points through xvalues[], to get the global vector x updated, you have to call <span style="color:rgb(0,0,0)">
</span>VecGhostUpdateBegin/End after above code, for example, to ADD two ghosts.</div>
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<pre>Does one need to call these two functions?<br></pre>
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<div>Yes. In PETSc, *Get and *Restore have to be paired.</div>
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