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<div dir="ltr">Is it because the array is already sorted?<br clear="all">
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<div dir="ltr">--Junchao Zhang</div>
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<div dir="ltr" class="gmail_attr">On Tue, Jul 2, 2019 at 12:13 PM Fande Kong via petsc-dev <<a href="mailto:petsc-dev@mcs.anl.gov">petsc-dev@mcs.anl.gov</a>> wrote:<br>
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<div dir="ltr">Hi Developers,<br>
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<div>John just noticed that the matrix assembly was slow when having sufficient amount of off-diagonal entries. It was not a MPI issue since I was able to reproduce the issue using two cores on my desktop, that is, "mpirun -n 2".</div>
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<div>I turned on a profiling, and 99.99% of the time was spent on PetscSortIntWithArrayPair (recursively calling). It took THREE MINUTES to get the assembly done. And then changed to use the option "-matstash_legacy" to restore </div>
<div>the code to the old assembly routine, and the same code took ONE SECOND to get the matrix assembly done. </div>
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<div>Should write any better sorting algorithms?</div>
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<div>Fande,</div>
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