[petsc-users] Matrix indexing for distributed DMPlex

[Matthew Kury]

Dear All, 

	I have been trying to figure out how to appropriately index a matrix that was created from a DMPlex with a section defined for it. 

	 I created the matrix with DMCreateMatrix() and I tried to index the entries by using the ISLocalToGlobalMapping obtained from DMGetLocalToGlobalMapping, with the local indices being those obtained from PetscSectionGetOffset() with the appropriate points from the D.A.G. However this does not seem to work. 

	In particular, with the  ISLocalToGlobalMapping, what I understand is that it gives the relationship of the local indexing to the global indexing, however there are negative numbers in this mapping which I fail to find an explanation of in the documentation. In addition, there do not appear to be redundant indexes to the global matrix as one would expect in a distributed DMPlex because there can be some of the same points on different processors. 

Any help is greatly appreciated. 

Thank you for your time, 


Matthew W. Kury
Ph.D. Candidate
CMRL UC Berkeley
M.S. Mechanical Engineering UC Berkeley, 2014






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