假設圖G 並不包含子圖C4，若在圖G 中任意不相鄰的兩點增加一邊後，就
會包含有子圖C4，那我們就稱圖G 為C4 飽和圖。令sat(n,C4)和ex(n,C4)分別代
表所有n 點C4 飽和圖中的邊數最小值與最大值。
在這篇論文中找到含有n 點C4 飽和圖的一種建構法，並給予含有n 點C4
飽和圖最少邊的一種建構法。再利用當n<=11 時C4 飽和圖的邊數之上、下界，
建構出其邊數介於sat(n,C4)和ex(n,C4)之間的n 點C4 飽和圖。接著應用圖的鄰接矩陣及C4 飽和圖的性質，利用Maple 判斷所產生的圖是否為C4 飽和圖。
我們定義了在完全多分圖中的C4 飽和圖，並探討完全多分圖Kn(m)的C4 飽
和圖中邊數最少的建構方式，得到以下結果：

1. sat(Kn,m, C4) <= m + n - 1，其中sat(Kn,m, C4) = min {│E(G)│: 圖G 為Kn,m 中C4 飽和圖}。
2. sat(Kn(m), C4) <= mn – 1 + ┌(n-2)/2┐*m, 其中sat(Kn(m), C4) = min {│E(G)│: 圖 G 為Kn(m) 中C4 飽和圖}，┌x┐為大於等於x 的最小整數值。

Let G be a graph. If there is no 4-cycle contained in G and connecting any non
adjacent vertices of G will obtain a 4-cycle, then we call G is a C4 saturated graph.
Let sat(n, C4) and ex(n, C4) be the minimum and maximum number of edges of all C4
saturated graphs with n vertices, respectively.
In this thesis, we obtain a construction of C4 saturated graph with n points, and
give another construction of C4 saturated graph with minimum edge. For n <= 11, we give a C4 saturated graph with n vertices and q edges, for each q between sat(n, C4)
and ex(n, C4). After that, we use Maple to check whether the graph is a C4 saturated graph by using the adjacency matrix of a graph and the properties of C4 saturated graphs.
We define a C4 saturated graph in a complete multipartite graph Kn (m) and obtain the following results:

1. sat(Kn,m, C4) <= m + n - 1; and
2. sat(Kn(m), C4) <= mn – 1 + ┌(n-2)/2┐*m, where sat(K, C4) = min {|E(G)|: G is a C4 saturated graph in the graph K} and ┌x┐ is the smallest integer greater than x .

目       錄


第一章	  簡介  ………………………………1
第二章	  基本定義  …………………………3
第三章	  含有n個點的C4飽和圖 …………8
第四章	  多分圖的C4飽和圖  ……………23
參考書目 ……………………………………34

參 考 書 目
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[10]Z. Tuza, C4-saturated graphs of minimum size, Acta Univ. Carolin. - Math. Phys. 30(1989)161-167.   
[11]Yang Yuansheng and P. Rowlinson,On extremal graphs without four-cycles, utilitas Mathematica 41(1992), 204-220.