BARORDER

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Choose automatically.

1 

Minimum degree method. This selects diagonal elements with the smallest number of nonzeros in their rows or columns.

2 

Minimum local fill method. This considers the adjacency graph of nonzeros in the matrix and seeks to eliminate nodes that minimize the creation of new edges.

3 

Nested dissection method. This considers the adjacency graph and recursively seeks to separate it into non-adjacent pieces.