# Functionality¶

`pymetis.``nested_dissection`(adjacency=None, xadj=None, adjncy=None)[source]

This function computes fill reducing orderings of sparse matrices using the multilevel nested dissection algorithm.

The input graph is given as either a Pythonic way as the adjacency parameter or in the direct C-like way that Metis likes as xadj and adjncy. It is an error to specify both graph inputs.

`pymetis.``part_graph`(nparts, adjacency=None, xadj=None, adjncy=None, vweights=None, eweights=None, recursive=None, contiguous=None)[source]

Return a partition (cutcount, part_vert) into nparts for an input graph.

The input graph is given in either a Pythonic way as the adjacency parameter or in the direct C-like way that Metis likes as xadj and adjncy. It is an error to specify both graph inputs.

The Pythonic graph specifier adjacency is required to have the following properties:

• len(adjacency) needs to return the number of vertices

• `adjacency[i]` needs to be an iterable of vertices adjacent to vertex i. Both directions of an undirected graph edge are required to be stored.

If you would like to use eweights (edge weights), you need to use the xadj/adjncy way of specifying graph connectivity. This works as follows:

The adjacency structure of the graph is stored as follows: The adjacency list of vertex i is stored in array adjncy starting at index `xadj[i]` and ending at (but not including) index ```xadj[i + 1]```. That is, for each vertex i, its adjacency list is stored in consecutive locations in the array adjncy, and the array xadj is used to point to where it begins and where it ends.

The weights of the edges (if any) are stored in an additional array called eweights. This array contains 2m elements (where m is the number of edges, taking into account the undirected nature of the graph), and the weight of edge `adjncy[j]` is stored at location `adjwgt[j]`. The edge-weights must be integers greater than zero. If all the edges of the graph have the same weight (i.e., the graph is unweighted), then the adjwgt can be set to `None`.

(quoted with slight adaptations from the Metis docs)

`pymetis.``verify_nd`(perm, iperm)[source]