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<div dir="ltr" class="gmail_attr">On Tue, Apr 30, 2019 at 11:42 AM Sajid Ali via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<br>
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<div>Hi PETSc Developers, <br>
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I see that in the examples for ISCreateGeneral, the index sets are created by copying values from int arrays (which were created by PetscMalloc1 which is not collective).
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<div>If I the ISCreateGeneral is called with PETSC_COMM_WORLD and the int arrays on each rank are independently created, does the index set created concatenate all the int-arrays into one ? If not, what needs to be done to get such an index set ?
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<div>From my understanding, they are independently created and not concatenated. I like index sets created with PETSC_COMM_SELF. They are easy to understand. </div>
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<div>PS: For context, I want to write a fftshift convenience function (like numpy, MATLAB) but for large distributed vectors. I thought that I could do this with VecScatter and two index sets, one shifted and one un-shifted.
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<div>To achieve this, index sets created with PETSC_COMM_SELF are enough. They just need to contain global indices to indicate the MPI vector to MPI vector scatter. You can think each process provides one piece of the scatter.</div>
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<div>Thank You,<br>
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<div style="font-size:12.8px">Sajid Ali<br>
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<div style="font-size:12.8px">Applied Physics<br>
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<div style="font-size:12.8px">Northwestern University</div>
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