Graphs in graph theory

**gallery of named graphs**
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English: Some of the finite structures considered in graph theory have names, sometimes inspired by the graph's topology, and sometimes after their discoverer. A famous example is the Petersen graph, a concrete graph on 10 vertices that appears as a minimal example or counterexample in many different contexts.^[1]

Individual graphs edit

Highly symmetric graphs edit

Strongly regular graphs edit

The strongly regular graph on v vertices and rank k is usually denoted srg(v,k,λ,μ).

Symmetric graphs edit

A symmetric graph is one in which there is a symmetry (graph automorphism) taking any ordered pair of adjacent vertices to any other ordered pair; the Foster census lists all small symmetric 3-regular graphs. Every strongly regular graph is symmetric, but not vice versa.

Semi-symmetric graphs edit

Graph families edit

Complete graphs edit

The complete graph on $n$ vertices is often called the $n$ -clique and usually denoted $K_{n}$ , from German komplett.^[2]

$K_{1}$
$K_{2}$
$K_{3}$
$K_{4}$
$K_{5}$
$K_{6}$
$K_{7}$
$K_{8}$

Complete bipartite graphs edit

The complete bipartite graph is usually denoted $K_{n,m}$ . The graph $K_{2,2}$ equals the 4-cycle $C_{4}$ (the square) introduced below.

$K_{2,3}$
$K_{3,3}$ , the utility graph
$K_{2,4}$
$K_{3,4}$

Cycles edit

The cycle graph on $n$ vertices is called the n-cycle and usually denoted $C_{n}$ . It is also called a cyclic graph, a polygon or the n-gon. Special cases are the triangle $C_{3}$ , the square $C_{4}$ , and then several with Greek naming pentagon $C_{5}$ , hexagon $C_{6}$ , etc.

$C_{3}$
$C_{4}$
$C_{5}$
$C_{6}$

Friendship graphs edit

The friendship graph F_n can be constructed by joining n copies of the cycle graph C₃ with a common vertex.^[3]

The friendship graphs F₂, F₃ and F₄.

Fullerene graphs edit

In graph theory, the term fullerene refers to any 3-regular, planar graph with all faces of size 5 or 6 (including the external face). It follows from Euler's polyhedron formula, $V-E+F=2$ (where $V,E,F$ indicate the number of vertices, edges, and faces), that there are exactly 12 pentagons in a fullerene and $V/2-10$ hexagons. Fullerene graphs are the Schlegel representations of the corresponding fullerene compounds.

20-fullerene (dodecahedral|dodecahedron|dodecahedral graph)
24-fullerene (hexagonal truncated trapezohedron graph)
26-fullerene
60-fullerene (truncated icosahedral graph)
70-fullerene

Platonic solids edit

The complete graph on four vertices forms the skeleton of the tetrahedron, and more generally the complete graphs form skeletons of simplices. The hypercube graphs are also skeletons of higher dimensional regular polytopes.

Cube
$n=8$ , $m=12$
Octahedron
$n=6$ , $m=12$
Dodecahedron
$n=20$ , $m=30$
Icosahedron
$n=12$ , $m=30$

Truncated Platonic solids edit

Snarks edit

A snark is a bridgeless cubic graph that requires four colors in any edge coloring. The smallest snark is the Petersen graph, already listed above.

Star edit

A star S_k is the complete bipartite graph K_1,k. The star S₃ is called the claw graph.

The star graphs S₃, S₄, S₅ and S₆.

Wheel edit

The wheel graph W_n is a graph on n vertices constructed by connecting a single vertex to every vertex in an (n-1)-cycle.

Wheels

W_{4}

–

W_{9}

.

References edit

↑ Gallery initially copied here from the English Wikipedia en:Gallery of named graphs, started there by en:User:Arbor on 16 June 2006
↑ David Gries and Fred B. Schneider, A Logical Approach to Discrete Math, Springer, 1993, p 436.
↑ Gallian, J. A. "Dynamic Survey DS6: Graph Labeling." Electronic J. Combinatorics, DS6, 1-58, Jan. 3, 2007. [1].

[1] Gallery initially copied here from the English Wikipedia en:Gallery of named graphs, started there by en:User:Arbor on 16 June 2006

[2] David Gries and Fred B. Schneider, A Logical Approach to Discrete Math, Springer, 1993, p 436.

[3] Gallian, J. A. "Dynamic Survey DS6: Graph Labeling." Electronic J. Combinatorics, DS6, 1-58, Jan. 3, 2007. [1].

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[2]

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