[petsc-users] ISGlobalToLocalMappingApplyBlock

Adrian Croucher a.croucher at auckland.ac.nz
Tue Nov 14 22:54:55 CST 2017


I'm trying to use ISGlobalToLocalMappingApplyBlock() and am a bit 
puzzled about the results it's giving.

I've attached a small test to illustrate. It just sets up a 
local-to-global mapping with 10 elements. Running on two processes the 
first has global indices 0 - 4 and the the second has 5 - 9. I then try 
to find the local index corresponding to global index 8.

If I set the blocksize parameter to 1, it correctly gives the results -1 
on rank 0 and 3 on rank 1.

But if I set the blocksize to 2 (or more), the results are -253701943 on 
rank 0 and -1 on rank 1. Neither of these are what I expected- I thought 
they should be the same as in the blocksize 1 case.

I'm presuming the global indices I pass in to 
ISGlobalToLocalMappingApplyBlock() should be global block indices (i.e. 
not scaled up by blocksize). If I do scale them up it doesn't give the 
answers I expect either.

Or am I wrong to expect this to give the same results regardless of 

Cheers, Adrian

Dr Adrian Croucher
Senior Research Fellow
Department of Engineering Science
University of Auckland, New Zealand
email: a.croucher at auckland.ac.nz
tel: +64 (0)9 923 4611

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