[petsc-users] Input arguments of DMPlexCreateFromDAG

[Cedric Doucet]

Hello, 
I tried to use DMPlexCreateFromDAG function to create a DM structure from a hybrid mesh. 
To understand how it works, I look at ex5.c file. 
Unfortunately, there are some things that I do not understand. 
1. Why does coneSize lists faces of cells first, then faces of vertices and finally faces of edges (in 2D)? Listing faces of vertices, then faces of edges and finally faces of cells is not simpler? 
2 What does coneOrientations contain? For two counterclockwise oriented triangles sharing an edge e={v0,v1}, I understand that {v0,v1} is the right oriented edge for the second triangle (and e for the first one) but what is the meaning of value -2? I read that it is -(o+1) with o=1 but why does o equal 1 in this case? 
Thank you very much for your help! 
Best regards, 
Cédric Doucet 

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