All Questions
Tagged with regular-graph graph-theory
14 questions
2
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1
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135
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Prove $G$ is regular if $d(u, v)$ is $x$ for adjacent $u$ and $v$ and is $y \ge 2$ otherwise
Prove $G$ is regular if $d(u, v)$ is $x$ for adjacent $u$ and $v$ and is $y \ge 2$ otherwise.
Here $d(u, v)$ denotes the number of common adjacent vertices between $u$ and $v$.
PS: I've been working ...
- 149
3
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1
answer
228
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Are "ultra-regular" bipartite graphs complete?
Let $X, Y$ be non-empty, disjoint sets and let $R\subseteq X\times Y$ be a binary relation. For $x\in X$, we set $R(x) = \{y\in Y: (x,y) \in R\}$ and for $y\in Y$, let $R^{-1}(y) = \{x\in X:(x,y)\in R\...
- 48.8k
2
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2
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123
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Existence of certain regular graphs
Question:
what can be said about the existence of $2k$ regular graphs, $1\lt k$ that have a $1$-factor and a $2$-factor?
Provided their existence, what is/are the smallest for $k$?
The graphs must be ...
- 13.2k
1
vote
1
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366
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Tree width and clique width of regular graphs
Consider a $k$ regular graph of $n$ vertices, where $3 \leq k \leq (n-1)$. Is there any upper or lower bound, in the worst case, known for either the tree-width or the clique width of each $k$ regular ...
1
vote
1
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187
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Deleting vertices of a regular graph to obtain a regular graph
Let $G$ be a symmetric $n$-regular graph. For which $k$ it is possible to delete some vertices from $G$ to obtain $k$-regular graph $G'$? For example, if $G$ is icosahedral graph (i.e. $5$-regular ...
- 691
5
votes
0
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154
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How to construct 4-regular graphs with few Hamiltonian decompositions?
A Hamiltonian decomposition of a finite simple graph is a partition of its edge set so that each partition class forms a Hamiltonian cycle. This is only possible if the graph is $2k$-regular.
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- 13.6k
2
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1
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391
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Maximum number of leaf blocks in 3-regular (cubic) graph
The definition of block is
Block of $G$ is a maximal subgraph $G'$ of $G$ with no cut vertex of $G'$ itself.
Of course, there can exist many blocks in $G$.
In particular, isolated vertices, edges in ...
- 341
3
votes
0
answers
99
views
If the girth of a $2k$-regular graph $G$ is larger than the diameter of a tree $T$ with $k$ edges, then $G$ is decomposed into copies of $T$
I want to prove that ‘If the girth of a $2k$-regular graph $G$ is larger than the diameter of a $k$-edge tree $T$, then $G$ is covered by edge-disjoint copies of $T$.’
I tried several ways to solve ...
- 341
2
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1
answer
489
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Is every $k$-edge connected $k$-regular graph Hamiltonian?
A graph $G$ is Hamiltonian if there is a Hamiltonian cycle in $G$.
Suppose $G$ is a $k$-edge connected $k$-regular graph with $k>1$.
Does this ensure that $G$ is Hamiltonian?
If not, how about ...
- 191
5
votes
2
answers
576
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Smallest $3$-regular graph with a unique perfect matching
What is the smallest 3-regular graph to have a unique perfect matching?
With a large enough number of nodes, it is possible for a 3-regular graph to have no perfect matching (example can be seen in ...
- 169
3
votes
2
answers
439
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Efficiently generating all regular/bidegreed graphs
There is a related question on how to generate all regular graphs; however, the procedure is random and repeats the generated graphs. Plus, there is no stop condition, unless recording the total ...
- 131
3
votes
0
answers
154
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Chromatic number of regular graphs using spectra
There exist inequalities relating the maximum and minimum eigenvalues of the adjacency matrix of a graph with its chromatic numbers, i.e. the Wilf's and Hoffmann's inequalities, which put together ...
- 2,089
0
votes
1
answer
157
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Decomposition of regular graphs
Let $G$ be a regular simple graph with degree $\Delta=n-k-1$ and order $m$. Let $C_k$ be the regular graph which is formed by removing a $k$-factor from the complete graph $K_{n}$. I think we could ...
- 2,089
1
vote
1
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171
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Lower bound for $\vert \det A \vert $ for the adjacency matrix of regular graphs
Assume $G$ is a simple $k$-regular graph of order $n$ with adjacency matrix $A$ which is non-singular.
Does anyone know some lower bounds for $\vert \det (A) \vert$ with respect to $n$, $k$ or both?
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