43 lines
1.6 KiB
Python
43 lines
1.6 KiB
Python
"""Utilities for constructing edge graphs from planar graphs."""
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from typing import Any, cast
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from sage.all import Graph
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def get_edge_graph_pos(edge_graph: Graph, pos_src: dict[Any, Any]) -> dict[Any, tuple[Any, Any]]:
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"""Return a position dict for edge graph vertices, using midpoints of the source positions."""
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pos: dict[Any, tuple[Any, Any]] = {}
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for e in cast(list[Any], edge_graph.vertices()): # type: ignore
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pos[e] = (
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(pos_src[e[0]][0] + pos_src[e[1]][0]) / 2,
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(pos_src[e[0]][1] + pos_src[e[1]][1]) / 2
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)
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return pos
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def get_edge_graph(graph: Graph, set_pos: bool = True) -> Graph:
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"""Return the edge graph of the given graph, optionally setting vertex positions."""
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pos_src: dict[Any, Any] | None = None
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pos: dict[Any, tuple[Any, Any]] = {}
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if set_pos:
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pos_src = cast(dict[Any, Any], graph.get_pos()) # type: ignore
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g = Graph()
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for e in cast(list[Any], graph.edges()): # type: ignore
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g.add_vertex(e) # type: ignore
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if pos_src:
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pos[e] = (
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(pos_src[e[0]][0] + pos_src[e[1]][0]) / 2,
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(pos_src[e[0]][1] + pos_src[e[1]][1]) / 2
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)
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for v in cast(list[Any], graph.vertices()): # type: ignore
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incident_edges = cast(list[Any], graph.edges_incident(v)) # type: ignore
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if len(incident_edges) == 1:
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continue
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for i, e1 in enumerate(incident_edges):
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e2 = incident_edges[(i + 1) % len(incident_edges)]
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g.add_edge(e1, e2) # type: ignore
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if set_pos:
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g.set_pos(pos) # type: ignore
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return g
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