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Plotting a LabelledOrderedTree with duplicate labels

asked 2019-08-08 14:05:02 -0600

nicklecoder gravatar image

updated 2019-08-28 03:23:57 -0600

FrédéricC gravatar image

I'm attempting to plot a labelled, ordered, rooted tree in Sage using the LabelledOrderedTree class. Here is what I have so far:

sage: n2 = LabelledOrderedTree([], label=2)
sage: n1 = LabelledOrderedTree([], label=1)
sage: root = LabelledOrderedTree([n2, n1], label=1)
sage: root
1[2[], 1[]]

At this point, I've created the tree I'm attempting to build, but here is where I run into problems:

sage: P = root.plot()
...
sage/graphs/base/sparse_graph.pyx in sage.graphs.base.sparse_graph.SparseGraphBackend.add_edge (build/cythonized/sage/graphs/base/sparse_graph.c:17158)()

ValueError: cannot add edge from 1 to 1 in graph without loops

Is there a way to plot a LabelledOrderedTree object when multiple nodes share the same label?

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answered 2019-08-09 13:13:18 -0600

rburing gravatar image

updated 2019-08-09 13:15:49 -0600

This (kind of silly) limitation is documented as a Warning.

Since you can use arbitrary objects as labels, here's a way around it:

class Wrap(object):
    def __init__(self, obj):
        self.obj = obj
    def __repr__(self):
        return repr(self.obj)

n2 = LabelledOrderedTree([], label=Wrap(2))
n1 = LabelledOrderedTree([], label=Wrap(1))
root = LabelledOrderedTree([n2, n1], label=Wrap(1))
root.plot()

image description

The two instances Wrap(1) and Wrap(1) are different Python objects, but they look the same, so it works.

Alternatively, if you want new distinct labels:

sage: root.canonical_labelling().plot()
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Comments

Thanks! Hadn't seen that warning, which also states one can alternatively use _latex_(), view, _ascii_art_(), or pretty_print as an alternative to obj.plot() as well. I personally think plot > view in terms of what the end result looks like, but at least it gives me something to work with.

nicklecoder gravatar imagenicklecoder ( 2019-08-09 14:33:54 -0600 )edit

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Asked: 2019-08-08 14:05:02 -0600

Seen: 53 times

Last updated: Aug 09