graph theory离散数学图论双语PPT文档格式.ppt
《graph theory离散数学图论双语PPT文档格式.ppt》由会员分享,可在线阅读,更多相关《graph theory离散数学图论双语PPT文档格式.ppt(112页珍藏版)》请在冰豆网上搜索。
![graph theory离散数学图论双语PPT文档格式.ppt](https://file1.bdocx.com/fileroot1/2022-10/5/2d2e0c09-4906-4646-9728-dd85b7fcc6df/2d2e0c09-4906-4646-9728-dd85b7fcc6df1.gif)
因為每次經過一個點,都需要從一條邊進入該點,再用另一條邊離開,所以經過每個點一次要使用掉一對邊。
每個點上連接的邊數必須是偶數才行此種走法不存在,Q:
是否存在一種走法,可以走過每條邊一次,並回到起點?
Ch1-5,Anelementaryexampleofgraphs,4students:
A,B,C,D4positions:
FF,SC,W,BS四人各有喜好的工作:
(如下圖,連線表示有興趣),Q:
Canallfourstudentsfindjobstheylike?
Ans:
No,(Ch6Matching),Ch1-6,Definitionofagraph,AgraphGisafinitenonemptysetV(G)ofvertices(alsocallednodes,點)anda(possiblyempty)setE(G)of2-elementsubsetsofV(G)callededges(orlines,邊).V(G):
vertexsetofG(只有一個G時常簡寫為V)E(G):
edgesetofG(只有一個G時常簡寫為E)常見的edge表示法:
u,v=v,u=uv(orvu)當邊有方向性時稱G為directedgraph(digraph),Ch1-7,Example,AgraphG=(V,E),whereV=u,v,w,x,y,zE=u,v,u,w,w,x,x,y,x,zE=uv,uw,wx,xy,xzG的diagram表示法:
Ch1-8,u,v:
verticesofagraphGuandvareadjacentinGifuvE(G)(uisadjacenttov,visadjacenttou)e=uv(ejoinsuandv)(eisincidentwithu,eisincidentwithv),AdjacentandIncident,Ch1-9,Graphstypes,undirectedgraph:
(simple)graph:
loop(),multiedge()multigraph:
loop(),multiedge()Pseudograph:
loop(),multiedge(),Ch1-10,orderandsize,ThenumberofverticesinagraphGiscalleditsorder(denotedby|V(G)|).Thenumberofedgesisitssize(denotedby|E(G)|).Proposition1:
If|V(G)|=pand|E(G)|=q,thenAgraphoforderpandsizeqiscalleda(p,q)graph.,Ch1-11,Applicationofgraphs,一群人間兩兩互相認識或不認識(i.e.,沒有A認識B但B不認識A的情形),在安排一張圓桌的晚餐座位時,是否存在一種排法能讓坐在一起的人都相互認識?
eg.Tom,DickknowSue,Linda.HarryknowsDickandLinda.,acquaintancegraph:
(連線表示認識),(Ch8Hamiltoniangraph),Q:
圖中是否有一個通過所有點的cycle?
Ch1-12,eg.Animals:
A,B,C,D,EAC不能與BD同區,E不能與其他動物同區,Applicationofgraphs,動物園要用圍牆劃分區域,避免同區的動物互相捕食,至少需分多少區?
Q:
將圖形的點著色(一色表示一區),若相鄰兩點需塗不同色,最少需多少顏色才夠?
3色3區,(Ch10GraphColoring),Ch1-13,Homework,Exercise1.1:
1,2,3,4,Ch1-14,Outline,1.1Whatisagraph?
1.2TheDegreeofaVertex1.3IsomorphicGraphs1.4Subgraphs1.5DegreeSequences1.6ConnectedGraphs1.7Cut-VerticesandBridges1.8Specialgraphs1.9Digraphs,Ch1-15,1.2Thedegreeofavertex,Definition.ForavertexvofG,itsneighborhoodN(v)=uV(G)|vuE(G).Thedegreeofvertexvisdeg(v)=|N(v)|.,N(u)=x,w,v,N(y)=,deg(u)=3,deg(y)=0,Ch1-16,Notes,If|V(G)|=p,then0deg(v)p-1,vV(G).Ifdeg(v)=0,thenviscalledanisolatedvertex(孤立點).visanoddvertexifdeg(v)isodd.visanevenvertexifdeg(v)iseven.,Ch1-17,Handshakingtheorem,Theorem1.1(Handshakingtheorem)LetGbeagraph,pf.在計算degree總和時,每條邊會被計算兩次。
Example,Ch1-18,Handshakingtheorem,Corollary1.1Everygraphcontainsanevennumberofoddvertices.,pf.Ifthenumberofverticeswithodddegreeisodd,thenthedegreesummustbeodd.,Ch1-19,Regulargraph,Definition.AgraphGisr-regularifeveryvertexofGhasdegreer.AgraphGisregularifitsr-regularforsomer.,2-regular,Note.Thereisno1-regulargraphor3-regulargraphoforder5.(byCorollary1.1),Example,Ch1-20,Complement,Definition.ThecomplementGofagraphGisagraphwithV(G)=V(G),anduvE(G)iffuvE(G).,Ch1-21,Applicationofdegree,Q:
npeople.(n2)Isitpossiblethateverytwoofthemareacquaintedwithadifferentnumberofpeopleinthegroup?
(SupposeifAknowsB,thenBknowsA.),A:
Considertheacquaintancegraph。
若任兩人所認識的人數不等,表示圖形中所有點的degree都不相等。
n點的圖形中,degree只可能是0,1,n-1(共n種),必有一點x的degree為0,另一點y的degree為n-1,也就是x不認識y,但y認識x,矛盾。
Ch1-22,Exercise1Provethateverygraphofordern2hasatleasttwoverticeswiththesamedegree.,pf.Ifnot,thenthereexistverticesxandywithdeg(x)=0anddeg(y)=n-1.Itsimpossible.,(Hint.Theprobleminpreviouspage.),Ch1-23,Exercise9.EveryvertexofagraphGoforder14andsize25hasdegree3or5.Howmanyverticesofdegree3doesGhave?
sol.Supposetherearexverticesofdegree3,thenthereare14-xverticesofdegree5.|E(G)|=25degreesum=503x+5(14-x)=50x=10,Ch1-24,Exercise10.AgraphGoforder7andsize10hassixverticesofdegreeaandoneofdegreeb.Whatisb?
sol.6a+b=20(a,b)=(0,20)()(1,14)()(2,8)()(3,2)()a=3,b=2.,Ch1-25,Homework,Exercise1.2:
4,7,11,Ch1-26,Outline,1.1Whatisagraph?
1.2TheDegreeofaVertex1.3IsomorphicGraphs1.4Subgraphs1.5DegreeSequences1.6ConnectedGraphs1.7Cut-VerticesandBridges1.8Specialgraphs1.9Digraphs,Ch1-27,1.3Isomorphicgraphs,v1,v3,v4,v5,u1,u2,u3,u4,u5,G1,G2,G1andG2arethesame(aftermovingsomevertices).,Ch1-28,Isomorphic,Definition.TwographG1andG2areisomorphic(同構)(denotedbyG1G2)ifthereisa1-1andontofunctionfromV(G1)toV(G2)suchthatuvE(G1)ifff(u)f(v)E(G2).(對應過去後,仍能保持兩點間相連與否的關係)Thefunctioniscalledanisomorphism.Inpreviouspage,f(vi)=uiforeachi.,Ch1-29,Isomorphic,Definition.TwographG1andG2areequalifV(G1)=V(G2)andE(G