[petsc-users] A number of questions about DMDA with SNES and Quasi-Newton methods

[zakaryah .]

Thanks Barry, that looks like exactly what I need.  I'm looking at pack.c
and packm.c and I want to check my understanding of what my coupling
function should do.  The relevant line in *DMCreateMatrix_Composite_AIJ *seems
to be:

(*com->FormCoupleLocations)(dm,NULL,dnz,onz,__rstart,__nrows,__start,__end);

and I infer that dnz and onz are the number of nonzero elements in the
diagonal and off-diagonal submatrices, for each row of the DMComposite
matrix.  I suppose I can just set each of these in a for loop, but can I
use the arguments to FormCoupleLocations as the range for the loop?  Which
ones - __rstart to __rstart+__nrows?  How can I determine the number of
rows on each processor from within the function that I pass?  From the
preallocation macros it looks like __start to __end describe the range of
the columns of the diagonal submatrix - is that right?  It looks like the
ranges will be specific to each processor.  Do I just set the values in dnz
and onz, or do I need to reduce them?

Thanks for all the help!  Maybe if I get things working I can carve out the
core of the code to make an example program for DMRedundant/Composite.
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