[問題] strongly connected directed

看板Prob_Solve (計算數學 Problem Solving)作者 (無法顯示)時間14年前 (2010/11/02 22:27), 編輯推噓1(106)
留言7則, 3人參與, 最新討論串1/1
consider a strongly connected directed graph G = (V,E), which has negative-length edges, but has no negative-length cycles let L(u, v) denote the length of an edge (u,v)屬於E, and d(u,v) denote the shortest path distance from vertex u to vertex v assume that a value s(v) is attached to each vertex v屬於V on the graph G consider a new graph G' that comes from transforming G by replacing the legth of each edge (u,v)屬於E with L(u,v) + s(u) - s(v) prove that the shortest path on the graph G' between w屬於V and x屬於V is also the shortest path between w and x on the graph G 請問這個問題要怎麼證明比較好? 謝謝 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 218.166.118.154

11/02 22:39, , 1F
想想 +s(u)-s(v) 的意義,一正一負是有原因的
11/02 22:39, 1F

11/03 19:23, , 2F
分項對消(?)
11/03 19:23, 2F

11/05 22:49, , 3F
就是 你可以看出來 對於圖中的任一條路徑
11/05 22:49, 3F

11/05 22:50, , 4F
其邊權和會是原本路徑的邊權和 加減某一常數
11/05 22:50, 4F

11/05 22:50, , 5F
所以最短路不變 (? 因為仍有最優子結構?
11/05 22:50, 5F

11/05 22:51, , 6F
啊...這樣講好怪ˊˋ 我再想想 抱歉orz
11/05 22:51, 6F

11/06 00:01, , 7F
CLRS的Johnson's algorithm for sparse graphs小節有證明過程
11/06 00:01, 7F
文章代碼(AID): #1Cq1_hnU (Prob_Solve)
文章代碼(AID): #1Cq1_hnU (Prob_Solve)