先说说什么叫稀疏矩阵。你说，这个问题很简单吗，那你一定不知道中国学术界的嘴皮子仗，对一个字眼的“抠”将会导致两种相反的结论。这是清华2000年的一道考研题：“表示一个有1000个顶点，1000条边的有向图的邻接矩阵有多少个矩阵元素？是否稀疏矩阵？”如果你是个喜欢研究出题者心理活动的人，你可以看出这里有两个陷阱，就是让明明会的人答错，我不想说出是什么，留给读者思考-First talk about what is meant by sparse matrix. You said that the issue it is very simple, you must do not know more than taking the academic battle in China, the word for a " dig out"　will lead to two opposite conclusion. This is the Tsinghua University in 2000 to join the study section of the title: " that a 1000 peak, while the 1000 has the adjacency matrix to map the number of matrix elements? Is sparse matrix?"　If you come up with a title like the psychological activities , you can see there are two traps is to let the people obviously got the wrong answer, I do not want to say what is left to readers to ponder