Graph Theory Quiz
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Questions and Answers

For definiteness, say G₁ and G₂ are the two ______.

components

The ______ Seven Bridge Problem is a classic problem in graph theory.

Konigsberg

The problem was to find a way to walk through all seven bridges without crossing any ______ more than once.

bridge

A graph G is ______ if and only if all circuits (cycles) in G are of even length.

<p>bipartite</p> Signup and view all the answers

Let V₁ and V₂ be the two sets of vertices in the ______, with every edge connecting one vertex from V₁ to a vertex from V₂.

<p>bipartition</p> Signup and view all the answers

If G is a ______ graph on n vertices, then n is of the type 4k or 4k + 1 for some integer k.

<p>self-complementary</p> Signup and view all the answers

A ______ graph G is a graph where, for every pair of vertices, there is at least one path connecting them.

<p>connected</p> Signup and view all the answers

The number of ______ components in graph is represented as W(G).

<p>connected</p> Signup and view all the answers

A graph G = (V, E) consists of a set V whose elements are called ______.

<p>vertices</p> Signup and view all the answers

An edge in a graph connects two vertices and is associated with an unordered pair, known as the ______ of the edge.

<p>end vertices</p> Signup and view all the answers

An edge whose end vertices are identical is called a ______.

<p>loop</p> Signup and view all the answers

If two edges share the same end vertices, they are referred to as ______ edges.

<p>parallel</p> Signup and view all the answers

A vertex with a degree of zero is called an ______.

<p>isolated vertex</p> Signup and view all the answers

The ______ is a principle stating that the sum of the degrees of all vertices in a graph equals twice the number of edges.

<p>Handshaking Lemma</p> Signup and view all the answers

A graph without loops and parallel edges is termed a ______.

<p>simple graph</p> Signup and view all the answers

In any graph, the number of odd vertices is ______.

<p>even</p> Signup and view all the answers

A subgraph obtained by deleting a vertex and all edges incident on it is called a ______ deleted subgraph.

<p>vertex</p> Signup and view all the answers

If U is a non-empty subset of the vertex set V, the subgraph G<U> is a ______ induced subgraph.

<p>vertex</p> Signup and view all the answers

If F is a non-empty subset of the edge set E, the subgraph G<F> is an ______ induced subgraph.

<p>edge</p> Signup and view all the answers

A ______ is defined as a finite alternating sequence of vertices and edges.

<p>walk</p> Signup and view all the answers

A ______ is a walk in which no edge is repeated.

<p>trail</p> Signup and view all the answers

A closed walk in which no vertex is repeated except terminal vertices is called a ______.

<p>cycle</p> Signup and view all the answers

A graph is called ______ if every two of its vertices are connected.

<p>connected</p> Signup and view all the answers

A graph G = (V, E) is called a null graph if the edge set E is ______.

<p>empty</p> Signup and view all the answers

If every vertex of graph G is of the same degree K, we say that G is ______-regular.

<p>K</p> Signup and view all the answers

A spanning subgraph of G is a subgraph H with V(H) = ______(G).

<p>V</p> Signup and view all the answers

Removing a single ______ will cause a disconnection in the network represented by graph G.

<p>pole</p> Signup and view all the answers

Let G be a graph. If the vertex set V of G can be partitioned into two non-empty subsets V₁ and V₂, then G is called a ______ Graph.

<p>Bipartite</p> Signup and view all the answers

A graph H = (V(H), E(H)) is called a subgraph of a graph G = (V(G), E(G)) if V(H) ⊆ ______(G) and E(H) ⊆ E(G).

<p>V</p> Signup and view all the answers

A proper subgraph H of G is defined as H ⊆ G but H ______ G.

<p>≠</p> Signup and view all the answers

In a complete graph, there is an edge between ______ pair of vertices.

<p>each</p> Signup and view all the answers

A simple graph G is not connected if there exists two vertices u and v in G such that there is no edge joining u and v. This means G is a _____ union of its subgraphs.

<p>disjoint</p> Signup and view all the answers

The complement graph G contains edges that are not present in G, which means for any edge e = (u, v), e ∉ E(G) implies e ∈ _____ G.

<p>E</p> Signup and view all the answers

According to Theorem 3, a graph G is connected if for every partition of its vertex set V(G) into two non-empty subsets V₁ and V₂, there exists an edge of G with one vertex in V₁ and another in _____

<p>V₂</p> Signup and view all the answers

If a graph has exactly two vertices of odd degree, then there must be a _____ between these two vertices.

<p>path</p> Signup and view all the answers

In the base case of the proof for Theorem 4, when m = 0, there are no edges, so the graph has n _____

<p>components</p> Signup and view all the answers

If G is disconnected, it can be expressed as a disjoint union of subgraphs, such as G equals G₁ union G₂. There does not exist an edge joining the vertex of G₁ and the vertex of _____

<p>G₂</p> Signup and view all the answers

The proof of Theorem 5 includes two cases: the first case considers G as being _____, which allows for a direct path between vertices.

<p>connected</p> Signup and view all the answers

Theorem 4 indicates that for a simple graph with n vertices, m edges, and k components, the inequality states n - k ≤ _____.

<p>m</p> Signup and view all the answers

Flashcards

Simple Graph

A graph where each edge connects two distinct vertices and there are no loops or multiple edges.

Multigraph

A graph that has loops or multiple edges connecting the same vertices.

Loop

An edge in a graph that connects a vertex to itself.

Parallel Edges

Two or more edges in a graph that have the same starting and ending vertices.

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Degree of a Vertex

The number of edges that are connected to a vertex.

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Isolated Vertex

A vertex that has no edges connected to it.

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Pendent Vertex

A vertex that has only one edge connected to it.

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Handshaking Lemma

The sum of the degrees of all vertices in a graph is equal to twice the number of edges.

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Null Graph

A graph with no edges.

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Complete Graph

A graph where every pair of vertices is connected by an edge.

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Regular Graph

A graph where every vertex has the same degree.

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Bipartite Graph

A graph whose vertices can be divided into two groups such that every edge connects a vertex in one group to a vertex in the other group.

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Spanning Subgraph

A subgraph that includes all the vertices of the original graph.

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Vertex Deleted Subgraph

A subgraph that includes all the vertices of the original graph except for one specific vertex.

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Edge Deleted Subgraph

A subgraph that includes all the vertices and all but one specific edge of the original graph.

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Even Vertex

A graph where every vertex has an even degree.

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Connected Graph

A graph is connected if there exists a path between every pair of vertices.

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Disconnected Graph

A graph is disconnected if there exists at least one pair of vertices without a path connecting them.

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Complement Graph

The complement of a graph G is a graph G' with the same vertex set as G, but where two vertices are adjacent in G' if and only if they are not adjacent in G.

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Partitioning a Connected Graph

A graph is connected if and only if for any partition of its vertices, there exists an edge connecting a vertex in one partition to a vertex in the other partition.

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Graph Components

The number of components in a simple graph is the minimum number of subgraphs required to cover all the vertices without any edges connecting them.

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Relationship Between Vertices, Edges, and Components

For any simple graph with n vertices, m edges, and k components, the number of vertices minus the number of components must be less than or equal to the number of edges.

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Odd Degree Vertex

A vertex in a graph is said to have an odd degree if it is connected to an odd number of edges.

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Path Between Odd Degree Vertices

A graph with exactly two vertices of odd degree must have a path connecting these two vertices.

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W(G)

The number of connected components in a graph.

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Self-Complementary Graph

A graph where the graph itself and its complement are isomorphic (identical structure).

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Konigsberg Seven Bridge Problem

A classic problem in graph theory that asks if a specific route can visit each bridge in a town once but only once.

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Theorem 7 (Self-Complementary Graphs)

The number of vertices in a self-complementary graph must be 4k or 4k + 1, where k is an integer.

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Vertex Induced Subgraph

A subgraph formed by selecting a subset of vertices and including all edges connecting those vertices within the original graph.

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Edge Induced Subgraph

A subgraph formed by selecting a subset of edges and including all vertices those edges connect in the original graph.

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Walk

A sequence of vertices and edges in a graph, where each edge connects two consecutive vertices in the sequence.

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Trail

A walk where no edge is repeated.

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Path

A walk where no vertex is repeated, except possibly the first and last vertex.

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Cycle (or Circuit)

A closed walk where no vertex is repeated, except the starting and ending vertex.

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Study Notes

Graph Theory

  • Graph theory differs from function graphs.
  • Informally, a graph consists of vertices and edges.
  • Vertices represent entities (e.g., people).
  • Edges connect vertices indicating a relationship.
  • Example applications include acquaintance, chemical bonding, electrical networks, and transportation networks.
  • Graph theory uses various techniques, including induction, parity, extremality, counting (in two ways), Pigeonhole Principle, and Inclusion-Exclusion principles.

Types of Graphs

  • Null graph (Nn): A graph with no edges.
  • Complete graph (Kn): A simple graph where each pair of distinct vertices is connected by an edge.
  • Regular graph: A graph where all vertices have the same degree.
  • Bipartite graph: A graph whose vertices can be divided into two disjoint sets such that every edge connects a vertex in one set to a vertex in the other set.

Elementary Terminologies and Results

  • End vertices: The vertices an edge connects.
  • Adjacent vertices: Vertices connected by an edge.
  • Loop: An edge whose both end nodes are the same.
  • Parallel edges: Two or more edges connecting the same pair of vertices.
  • Degree (or valency) of a vertex: The number of edges incident on the vertex. A loop contributes 2 to the degree of the vertex.
  • Isolated vertex: A vertex with a degree of zero.
  • Pendent vertex: A vertex with a degree of one.
  • Simple graph: A graph with no loops and no parallel edges.
  • Multigraph: A graph that can have parallel edges or loops.
  • (n, m) graph: A graph with n vertices and m edges.

Theorem 1 (Handshaking Lemma)

  • The sum of the degrees of all vertices in a graph equals twice the number of edges.

Special Graphs

  • Null graph Nn: Graph with n vertices and no edges.

  • Complementary graph: G' is the complementary graph of G, where there is an edge between two vertices in G' if there is no corresponding edge in G.

Connected Graphs

  • Connected graph: A graph where there is a path between every pair of vertices.

  • Disconnected graph: A graph that contains at least two disconnected components

Walk, Trail, and Cycle in a Graph

  • Walk: A sequence of vertices and edges where each edge connects consecutive vertices.
  • Trail: A walk in which no edge is repeated. Repetition of vertices is allowed.
  • Path: A trail where no vertex is repeated.
  • Cycle: A closed walk or trail that starts and ends at the same vertex.

Induced Subgraphs

  • Induced Subgraph (G[U]): Subgraph of G where only the vertices in U and edges determined by them are included.
  • Vertex deletion: (G -v): Subgraph of G after removing vertex v and all incident edges.
  • Edge deletion: (G -e) Subgraph of G after removing edge e and preserving all other vertices.

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Description

Test your knowledge on graph theory concepts and terminology with this engaging quiz. Topics include the Seven Bridge Problem, types of graphs, vertices, edges, and components within graphs. Challenge yourself and deepen your understanding of this fundamental area in mathematics.

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