Common Graph Classes and Their Properties
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Questions and Answers

What is the key assumption made to prove that a graph without odd cycles is bipartite?

  • The graph has a minimum length path between any two vertices
  • The graph has no odd cycles (correct)
  • The graph is nontrivial
  • The graph is connected
  • Why is the cycle formed by combining a u-v path, edge vw, and a w-u path of minimum length an odd cycle in the proof?

  • Because the edge vw is of odd length
  • Because the sum of the lengths of the u-v path, vw edge, and w-u path is odd (correct)
  • Because the u-v and w-u paths are of even length
  • Because the u-v and w-u paths are of odd length
  • In the Cartesian product G□H, what determines whether an edge connects vertices (u, x) and (v, y)?

  • Whether u and v are adjacent in G and x and y are adjacent in H
  • Whether u = x and v = y, or u = y and v = x, or u = v and x = y
  • Whether either u = x and v = y, or u = y and v = x
  • Whether u and v are adjacent in G or x and y are adjacent in H (correct)
  • What is the key idea behind proving that there is no graph of order n ≥ 2 whose vertices have all different degrees?

    <p>Using the Pigeonhole Principle to show that at least two vertices must have the same degree (D)</p> Signup and view all the answers

    Which of the following best describes the concept of the join of two graphs G and H, denoted G + H?

    <p>A graph that consists of vertices from both G and H, with edges connecting all vertices in G to all vertices in H (D)</p> Signup and view all the answers

    What is the size of the complete graph Kn?

    <p>$\frac{n(n-1)}{2}$ (C)</p> Signup and view all the answers

    What is the relationship between the size of a graph G and its complement ?

    <p>The size of <em>G</em> plus the size of <em>Ḡ</em> equals the size of a complete graph with the same order. (B)</p> Signup and view all the answers

    What is the order of the empty graph n?

    <p>n (A)</p> Signup and view all the answers

    Which of the following statements is TRUE for bipartite graphs?

    <p>Bipartite graphs cannot contain any odd cycles. (D)</p> Signup and view all the answers

    What is the relationship between the degree of a vertex in a graph G and its degree in the complement ?

    <p>The degree in <em>Ḡ</em> equals the order of the graph minus one minus the degree in <em>G</em>. (D)</p> Signup and view all the answers

    If a graph has an odd number of vertices, is it possible for it to be bipartite?

    <p>Yes, it's possible for any graph with an odd number of vertices to be bipartite. (C)</p> Signup and view all the answers

    What is a path graph?

    <p>A graph where the vertices can be arranged in a linear sequence, with each vertex connected to the adjacent vertices. (A)</p> Signup and view all the answers

    What is the order of a cycle graph Cn?

    <p>n (C)</p> Signup and view all the answers

    Study Notes

    Common Graph Classes

    • Paths: A graph is a path if its vertices can be relabeled as u₁, u₂, ..., uₙ so that the edges are u₁u₂, u₂u₃, ..., uₙ₋₁uₙ. A path of order n is denoted by Pₙ.
    • Cycles: A graph of order n ≥ 3 is a cycle if its vertices can be relabeled as u₁, u₂, ..., uₙ so that the edges are u₁u₂, u₂u₃, ..., uₙ₋₁uₙ, and uₙu₁. A cycle of order n is denoted by Cₙ.
    • Complete Graphs: A graph is complete if every pair of distinct vertices is adjacent. A complete graph of order n is denoted by Kₙ. The size (m) of a complete graph of order n is given by m = n(n-1)/2.

    Complement of a Graph

    • The complement of a graph G, denoted as Ḡ, is the graph with the same vertices as G. An edge exists between two vertices in Ḡ if and only if there is no edge between those vertices in G.

    Bipartite Graphs

    • A graph is bipartite if its vertices can be partitioned into two sets (A and B) such that no edge connects two vertices within the same set.

    Theorem 1.12

    • A nontrivial graph is bipartite if and only if it contains no odd cycles.

    Definitions and Notation

    • Join (G + H): If G and H are graphs, their join (G + H) is the graph that combines G and H, along with all edges connecting a vertex in G to a vertex in H.
    • Cartesian Product (G × H): If G and H are graphs, their Cartesian product (G × H) is a graph where vertices are pairs of vertices from G and H, and two vertices are connected if either their first components are the same and their second components are connected in H or their second components are the same and their first components are connected in G.

    Problem

    • The provided image shows examples of finding the Cartesian product and the join of two graphs (P₃ and K₃).

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    Description

    This quiz covers various classes of graphs, including paths, cycles, complete graphs, and bipartite graphs. It also discusses the complement of a graph and relevant theorems associated with these concepts. Test your understanding of graph theory and its fundamental concepts through this engaging quiz.

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