Lx=d: SundayResearch

I first met C three months ago. I teach her one digit plus, like 3+4. One digit plus is somewhat OK for her, but, two digits were hard to her.  If I taught slowly, she could do it. However, next week she glanced at the same problem, then she said ``Geht's nicht (Can't be!)' and she immediately gave up. The whole month was like that. I thought, ``I see, she is a tough one.'' I told her every time, ``Mathematics is a language. It is a reflection of human mind. Maybe this doesn't make sense for you, but, it's a language. Which means there is a meaning of all of them. So what does it mean 3+4?'' One day, I used a drawing, the other day, I used a block to explain the numbers and plus. I try to show that we can touch the numbers. However, what she wanted know was the answers of her homework. Once she cried that she needed to fill the homework until tomorrow. I felt sorry a bit, but, I said ``The answer is not important. Your understanding is important....

L is not a so diligent girl. But she sometimes finishes the exercise very quickly. Although I found she repeatedly mistook the same problem. For example, in one exercise, 4+7 was always 12. I asked what is equal to 4 + 7. She used fingers, took a little while, but she answered correctly at the end. Then I noticed, ``Wait, if she solve the problem with this speed, how she can finish the exercise so quickly?'' So, I sat down next to her and watched how she solved the problem. Surprise! She doesn't calculate at all. She just looks up the last pages and copies the answers. What I was impressed was she was so fast. She was faster than me to look up the questions. I understood why she made the same mistakes again and again. I learned a new German sentence, ``Bitte nicht angucken!'' This means, ``Don't cheat by looking.'' though it's hard to translate to English. Her speed of cheating is impressive, this might be her talent. I don't know that I sha...

To remove the KDE Wallet popup when I logged in in Kubuntu 12.04. Install the kwalletmanager.  (This is the tricky part, if you deinstall  it you can not disable it. ) Open KDE-system settings, Open Account details -- KDE Wallet (If you didn't install it, you don't see the KDE wallet.) Uncheck Enable the KDE wallet subsystem. Because the popup is caused by kwalletd, that is kde's base runtime, so you can not remove it as long as you use kde. The deinstalling kwalletmanager only removes its GUI and tools, the subsystem is there. Therefore, deinstall the kwalletmanager doesn't help. KDE Wallet service popup window which I want to disable Thanks to Joerg who told me there is a way to disable this.

Abstract One of my favorite column is ACM's Kode Vicious (e.g., http://doi.acm.org/10.1145/1364782.1364791 ). I am also a developer, and I am sure that I encounter the bugs that makes his blood pressure high. This bug was ``a global static destructor is called twice.'' Contents I basically avoid to write a code that has static objects. Because static objects has a side effect and also their construction and destruction order is not under the programmer's control in C++ language. Then, why I encounter this bug? Well, I didn't write it at the first  place. But I can not avoid since it is a part of my job. I found my crash is caused by a static destructor is called twice. I first thought, the stack is corrupted, since I didn't know it is possible except the compiler bug. In C++, static object constructed and destructed only once, the constructor is called before the main function starts, and the destructor is called after main function finished. The number ...

The adjacency matrix A matrix  is a two-dimensional rectangular array of numbers arranged in rows and columns. It looks like a table of numbers. The readers who want to more about matrix, see the Appendix A (will be shown up the later blog) in this document as a short introduction, or to know more deeply, see [7]. I would like to show how a matrix can be used to describe a graph. My motivation is to be able to write down a graph. Following some rules, we can write down a graph in matrix form. Let me introduce such a method for representing a graph here. The matrix I will describe is called an adjacency matrix . Definition :  An adjacency matrix \(A\) of a graph of \(N\) vertices is an \(N \times N\) matrix where the element \(a_{i,j}\) is 1 when there is a directed edge from node \(i\) of the graph to node \(j\), otherwise 0. That's all there is to it. An element in an adjacency matrix that represents a connection is a 1; an element that represents the lack of a con...