#18317: General documentation about graph data structures
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Reporter: | Owner:
ncohen | Status: needs_review
Type: | Milestone: sage-6.7
enhancement | Resolution:
Priority: major | Merged in:
Component: graph | Reviewers:
theory | Work issues:
Keywords: | Commit:
Authors: | 8d61e569bfd222ee604bf433bf557ac88469518c
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
public/18317 |
Dependencies: |
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Comment (by darij):
Just commenting...
In `src/sage/graphs/base/overview.py`, you mention digraphs, but you seem
to say nothing about them.
"Supports: addition/removal of edges/vertices available": remove the
"available"?
"ligther" should be "lighter".
There is yet another distinction that is often left implicit but needs to
be clarified here: In a graph, the edges can be either just predicates
saying that "vertex `a` is connected to vertex `b`, (possibly) with edge
label `l`", or they can be mathematical objects on their own rights. The
difference is most obvious when you have two edges with the same label
both from a vertex `a` to a vertex `b`. Are these two edges equal or not?
In the first case, they are (i.e., we've got one edge appearing twice in
the edge multiset), while in the second case, they're not (i.e., we have
two edges which just happen to have the same `a`, the same `b`, and the
same label). The second viewpoint is important in homology, category and
quiver theory (e.g., to make sense of a cycle basis of a multigraph, edges
would have to have their own identities), whereas the first one seems to
be a thing among graph theorists. A doc should make clear which of them is
supported by which class.
--
Ticket URL: <http://trac.sagemath.org/ticket/18317#comment:2>
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