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labeled graph (Definition)

Let $ G=(V,E)$ be a graph with vertex set $ V$ and edge set $ E$. A labeling of $ G$ is a partial function $ \ell: V\cup E\to L$ for some set $ L$. For every $ x$ in the domain of $ \ell$, the element $ \ell(x)\in L$ is called the label of $ x$. Three of the most common types of labelings of a graph $ G$ are

  • total labeling: $ \ell$ is a total function (defined for all of $ V\cup E$),
  • vertex labeling: the domain of $ \ell$ is $ V$, and
  • edge labeling: the domain of $ \ell$ is $ E$.
Usually, $ L$ above is assumed to be a set of integers. A labeled graph is a pair $ (G,\ell)$ where $ G$ is a graph and $ \ell$ is a labeling of $ G$.

An example of a labeling of a graph is a coloring of a graph. Uses of graph labeling outside of combinatorics can be found in areas such as order theory, language theory, and proof theory. A proof tree, for instance, is really a labeled tree, where the labels of vertices are formulas, and the labels of edges are rules of inference.

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"labeled graph" is owned by CWoo.
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Other names:  labelled graph, graph labelling, labelling, vertex labelling, edge labelling, total labelling, labelled tree, labelled multigraph, labelled pseudograph
Also defines:  graph labeling, labeling, vertex labeling, edge labeling, total labeling, labeled tree, labeled multigraph, labeled pseudograph
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Cross-references: pseudographs, multigraphs, digraphs, rules of inference, tree, language, theory, order, areas, coloring, integers, total function, types, label, domain, partial function, edge, vertex, graph
There are 14 references to this entry.

This is version 3 of labeled graph, born on 2007-11-25, modified 2007-11-26.
Object id is 10060, canonical name is LabeledGraph.
Accessed 1604 times total.

Classification:
AMS MSC05C78 (Combinatorics :: Graph theory :: Graph labelling )

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