get graph combinatorial embedding from position of vertices

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Hmmmmm.. Well it seems that obtaining the embedding from the positions is notimplemented yet (and it should not be complicated, so you are welcome to add it if you need it !), but you can obtain an embedding from a call to is_planar. This will give you a planar embedding, though it will use its own layout for the vertices of your graph.

sage: g=graphs.IcosahedralGraph()
sage: g.get_embedding()
...
ValueError: Icosahedron has been modified and the embedding is no longer valid
sage: g.is_planar(set_embedding=True)
True
sage: g.get_embedding()
{0: [1, 5, 11, 7, 8],
 1: [8, 2, 6, 5, 0],
 2: [8, 9, 3, 6, 1],
 3: [2, 9, 10, 4, 6],
 4: [3, 10, 11, 5, 6],
 5: [0, 1, 6, 4, 11],
 6: [1, 2, 3, 4, 5],
 7: [0, 11, 10, 9, 8],
 8: [0, 7, 9, 2, 1],
 9: [8, 7, 10, 3, 2],
 10: [9, 7, 11, 4, 3],
 11: [0, 5, 4, 10, 7]}

I am also having trouble with set_embedding. My Graph does not have a unique planar embedding, and I would like to set the embedding to a different one from that found by sage.

sage: D3half2=Graph({0:{1:'x2', 2:'x8', 3:'x9', 4:'x5'}, 1:{2:'x3'}, 2:{3:'x6', 4:'x4'}, 3:{4:'x12', 5:'x10'}, 4:{5:'x11'}})

sage: D3half2.is_planar()

True

sage:D3half2.is_planar(set_embedding=True) D3half2.set_embedding({0:{1, 4, 3, 2}, 1:{2, 0}, 2:{1, 0, 3, 4}, 3:{2, 0, 4, 5}, 4:{2, 5, 3, 0}})

ValueError Traceback (most recent call last) <ipython-input-11-78d1277ebcd7> in <module>() ----> 1 D3half2.set_embedding({Integer(0):{Integer(1), Integer(4), Integer(3), Integer(2)}, Integer(1):{Integer(2), Integer(0)}, Integer(2):{Integer(1), Integer(0), Integer(3), Integer(4)}, Integer(3):{Integer(2), Integer(0), Integer(4), Integer(5)}, Integer(4):{Integer(2), Integer(5), Integer(3), Integer(0)}})

/opt/sagemath-9.1/local/lib/python3.7/site-packages/sage/graphs/generic_graph.py in set_embedding(self, embedding) 2501 ValueError: vertices in ['s'] from the embedding do not belong to the graph 2502 """ -> 2503 self._check_embedding_validity(embedding, boolean=False) 2504 self._embedding = embedding 2505

/opt/sagemath-9.1/local/lib/python3.7/site-packages/sage/graphs/generic_graph.py in _check_embedding_validity(self, embedding, boolean) 2589 raise ValueError("vertices in {} from the embedding do not belong to the graph".format(list(set(embedding).difference(self)))) 2590 else: -> 2591 raise ValueError("vertices in {} have no corresponding entry in the embedding".format(list(set(self).difference(embedding)))) 2592 2593 if self._directed:

ValueError: vertices in [5] have no corresponding entry in the embedding

Thanks for any help!!!!