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The Lumenary
الصفوف 9–12Discrete Mathematicsمُخطَّط له

Graphs

Graphs as vertices and edges, degree and the handshake lemma, paths and connectivity, Euler circuits, trees and graph isomorphism.

math.discrete.graph-basics

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عدد المتطلبات السابقة الإلزامية (حتى الأساس): 11

ستتعلّم

  • Prove the handshake lemma and Euler's criterion for Eulerian circuits.
  • Prove that a tree with n vertices has n − 1 edges.
  • Decide whether two small graphs are isomorphic.

تعريف

  • A simple graph consists of a set V of vertices and a set E of two-element subsets of V, called edges.
  • A tree is a connected graph with no cycles.
  • Graphs G and H are isomorphic if there is a bijection between their vertex sets that preserves adjacency in both directions.

مبرهنة

  • Handshake lemma: the sum of the degrees of all vertices is 2|E|.
  • A connected graph has an Eulerian circuit if and only if every vertex has even degree.
  • A tree on n vertices has exactly n − 1 edges, and any two of its vertices are joined by a unique path.

مفاهيم خاطئة شائعة

  • Thinking a particular drawing determines the graph; very different drawings can show the same graph.
  • Confusing Euler circuits (using each edge once) with Hamiltonian cycles (visiting each vertex once).

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اكتشافات اختيارية

مسارات التعلّم

قراءات إضافية

  • J. A. Bondy and U. S. R. Murty, Graph Theory with Applications (1976)