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# `altgraph.GraphUtil` — Utility functions

The module `altgraph.GraphUtil` performs a number of more or less useful utility functions.

`altgraph.GraphUtil.``generate_random_graph`(node_num, edge_num[, self_loops[, multi_edges])

  Generates and returns a `Graph` instance with node_num nodes randomly connected by edge_num edges.

  When self_loops is present and True there can be edges that point from a node to itself.

  When multi_edge is present and True there can be duplicate edges.

  This method raises `GraphError <altgraph.GraphError` when a graph with the requested configuration cannot be created.

`altgraph.GraphUtil.``generate_scale_free_graph`(steps, growth_num[, self_loops[, multi_edges]])

  Generates and returns a `Graph` instance that will have steps*growth_n um nodes and a scale free (powerlaw) connectivity.

  Starting with a fully connected graph with growth_num nodes at every step growth_num nodes are added to the graph and are connected to existing nodes with a probability proportional to the degree of these existing nodes.

  Warning

  The current implementation is basically untested, although code inspection seems to indicate an implementation that is consistent with the description at Wolfram MathWorld

`altgraph.GraphUtil.``filter_stack`(graph, head, filters)

  Perform a depth-first oder walk of the graph starting at head and apply all filter functions in filters on the node data of the nodes found.

  Returns (visited, removes, orphans), where

  - visited: the set of visited nodes
  - removes: the list of nodes where the node data doesn’t match all filters.
  - orphans: list of tuples (last_good, node), where node is not in removes and one of the nodes that is connected by an incoming edge is in removes. Last_good is the closest upstream node that is not in removes.

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