Graph coloring problem
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The document discusses graph coloring and its applications. It defines graph coloring as assigning colors to graph vertices such that no adjacent vertices have the same color. It also discusses the four color theorem, which states that any planar map can be colored with four or fewer colors. Finally, it provides an overview of backtracking as an algorithmic approach for solving graph coloring problems.
Graph coloring problem
- 1. Mrs.G.Chandraprabha,M.Sc.,M.Phil., Assistant Professor Department of IT V.V.Vanniaperumal College for Women Virudhunagar Graph Coloring problem Using Backtracking
- 2. Graph Coloring is an assignment of colors (or any distinct marks) to the vertices of a graph. Strictly speaking, a coloring is a proper coloring if no two adjacent vertices have the same color. SGVf )(:
- 3. Definition: A graph is planar if it can be drawn in a plane without edge-crossings. The four color theorem: For every planar graph, the chromatic number is ≤ 4.
- 4. The four color theorem states that any planar map can be colored with at most four colors. In graph terminology, this means that using at most four colors, any planar graph can have its nodes colored such that no two adjacent nodes have the same color. Four-color conjecture – Francis Guthrie, 1852 (F.G.) Many incomplete proofs (Kempe). 5-color theorem proved in 1890 (Heawood) 4-color theorem finally proved in 1977 (Appel, Haken) ◦ First major computer-based proof
- 5. A vertex coloring is an assignment of labels or colors to each vertex of a graph such that no edge connects two identically colored vertices
- 6. Similar to vertex coloring, except edges are color. Adjacent edges have different colors.
- 7. Every edge-coloring problem can be transformed into a vertex-coloring problem Coloring the edges of graph G is the same as coloring the vertices in L(G) Not every vertex-coloring problem can be transformed to an edge-coloring problem Every graph has a line graph, but not every graph is a line graph of some other graph
- 8. K-Coloring ◦ A k-coloring of a graph G is a mapping of V(G) onto the integers 1..k such that adjacent vertices map into different integers. ◦ A k-coloring partitions V(G) into k disjoint subsets such that vertices from different subsets have different colors.
- 9. K-colorable ◦ A graph G is k-colorable if it has a k-coloring. Chromatic Number ◦ The smallest integer k for which G is k-colorable is called the chromatic number of G, is denoted by the χ(G).
- 10. The idea is to assign colors one by one to different vertices, starting from the vertex 0. Before assigning a color, we check for safety by considering already assigned colors to the adjacent vertices. If we find a color assignment which is safe, we mark the color assignment as part of solution. If we do not a find color due to clashes then we backtrack and return false. Backtracking Algorithm
- 11. NP: the class of decision problems that are solvable in polynomial time on a nondeterministic machine (or with a nondeterministic algorithm) (A deterministic computer is what we know) A nondeterministic computer is one that can “guess” the right answer or solution think of a nondeterministic computer as a parallel machine that can freely spawn an infinite number of processes Thus NP can also be thought of as the class of problems whose solutions can be verified in polynomial time Note that NP stands for “Nondeterministic Polynomial-time”
- 12. Fractional Knapsack Sorting Others? ◦ Graph Coloring ◦ Satisfiability (SAT) the problem of deciding whether a given Boolean formula is satisfiable.
- 13. Many problems can be formulated as a graph coloring problem including Time Tabling, Scheduling, Register Allocation, Channel Assignment. A lot of research has been done in this area so much is already known about the problem space.
- 14. Thank You