# Tag Info

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The most common way to write finite element software is to make a non-overlapping partition of elements with interface vertex ownership resolved using some rule (or via hypergraph partitioning, which is more expensive). To create a globally-assembled stiffness matrix, this involves communication of entries to the process that owns the vertex. Residual ...

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If different nodes have different costs, for example because different rows of your matrix have different numbers of nonzero entries, then you need to attach weights to each node of your graph. Graph partitioning algorithms such as METIS allow you to do this, creating partitions where it is not the number of nodes that are about equal between partitions, but ...

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For your first question, constructing the adjacency graph of the "partitions" (what you call "cell groups"): Let's say you have an array $p_K$ in which you store for each cell $K$ which partition $p$ it belongs to. Also assume that you have a (sparse) array $a_{KL}$ whose entries are true if cells $K$ and $L$ are neighbors ("adjacent&...

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If I understand what you're looking for correctly, it looks like you want to compute the contour lines of constant BMI and use those as boundaries to separate your domain? A very simple algorithm for approximating this is the marching squares algorithm. The general premise of the algorithm is you discretize your domain into a grid of rectangular cells and ...

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You need to look up the VTK file format here: https://vtk.org/wp-content/uploads/2015/04/file-formats.pdf It's not very difficult, you'd just write a single cell for each node of your quad tree. The results will look like the pictures you see here or here or here -- all use VTK file format to visualize meshes.

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Your intuition is correct -- a bisection method cuts the (hyper)graph in two, and recursive bisection repeatedly applies this strategy until the desired number of cuts have been made. Direct partitioning on the other hand tries to immediately divide up the graph. Part of the divide between the two is historical. Some of the earliest successful heuristics ...

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Consider the following visualization as an example. It visualizes two binary trees: $T_S$ and $T_V$ for the surface mesh of the sphere and volume mesh of the sphere, respectively. At the 0th level, there is only one node in each tree: $S_1^{(0)}$ and $V_1^{(0)}$. The superscript in the brackets denotes the level in the tree and the subscript denotes the ...

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For a simple (yet not optimal, see below) mesh partitioning algorithm, you can do: 1) sort all the cells of the mesh using Hilbert sort 2) partition the sorted list of cells into chunks of the desired size Spatial Hilbert sorting is implemented in my GEOGRAM library [1,2] and in CGAL . It is reasonably easy to implement, using the std::nth_element() ...

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Check out: Nijboer, B. R. A., & De Wette, F. W. (1957). On the calculation of lattice sums. Physica, 23(1-5), 309–321. doi:10.1016/S0031-8914(57)92124-9 There they make the case for using a splitting based on the incomplete Gamma function. That splitting generalizes the choice of the error function to arbitrary dimensions.

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I was having an issue with Metis_PartMeshDual where if my number of processors was greater than (number of elements)/2 I would get processors that were given no elements. I believe this is what the OP means by a partition getting an "empty subdomain". I found that the line options[METIS_OPTION_PTYPE] = METIS_PTYPE_RB; made it so that for all cases ...

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