Interesting ideas in CACM (Vol.55, No.9)

I found two interesting ideas in CACM, Vol.55, No.9.

1. DieHard

Many C++ program's crash bugs are caused by small out of bound access. So, if a memory allocator gives a slightly large memory chunk, also randomize the heap allocation. Then many bugs become non-deterministic, Heisenberg bug.

This is a nightmare for developers who should fix this kind of bugs. Because, it is hard to catch the bug.

However, for some users, this might be better. If one just restarts the program, the crash may be gone if they are lucky.

You can find this idea entitled DieHard from Microsoft research. Although, I don't think randomly hiding bugs are analogy of Seat belts or Airbags. I found this idea interesting, but I prefer deterministic bugs as a developer. Also I prefer to fix the bugs rather than hiding them.

http://queue.acm.org/detail.cfm?id=2333133

2. CriptDB

I heard some methods that you can search encrypted data without decrypt it or search a compressed data without decompress it. I don't understand the details, but the basic idea is having a kind of data onto map function. For example, I have a database which contains English text. I encrypt this database by translating German. So if anyone who don't know German can not read the database. If I want to search a word ``mountain'', then ``mountain'' is encrypted as ``Berg'', the I search the word ``Berg''. The story is also not so simple, however, the basic idea seems like this.

http://dl.acm.org/citation.cfm?doid=2330667.2330691

Comments

Why A^{T}A is invertible? (2) Linear Algebra

Why A^{T}A has the inverse Let me explain why A^{T}A has the inverse, if the columns of A are independent. First, if a matrix is n by n, and all the columns are independent, then this is a square full rank matrix. Therefore, there is the inverse. So, the problem is when A is a m by n, rectangle matrix. Strang's explanation is based on null space. Null space and column space are the fundamental of the linear algebra. This explanation is simple and clear. However, when I was a University student, I did not recall the explanation of the null space in my linear algebra class. Maybe I was careless. I regret that... Explanation based on null space This explanation is based on Strang's book. Column space and null space are the main characters. Let's start with this explanation. Assume x where x is in the null space of A . The matrices ( A^{T} A ) and A share the null space as the following: This means, if x is in the null space of A , x is also in the n...

Gauss's quote for positive, negative, and imaginary number

Recently I watched the following great videos about imaginary numbers by Welch Labs. https://youtu.be/T647CGsuOVU?list=PLiaHhY2iBX9g6KIvZ_703G3KJXapKkNaF I like this article about naming of math by Kalid Azad. https://betterexplained.com/articles/learning-tip-idea-name/ Both articles mentioned about Gauss, who suggested to use other names of positive, negative, and imaginary numbers. Gauss wrote these names are wrong and that is one of the reason people didn't get why negative times negative is positive, or, pure positive imaginary times pure positive imaginary is negative real number. I made a few videos about explaining why -1 * -1 = +1, too. Explanation: why -1 * -1 = +1 by pattern https://youtu.be/uD7JRdAzKP8 Explanation: why -1 * -1 = +1 by climbing a mountain https://youtu.be/uD7JRdAzKP8 But actually Gauss's insight is much powerful. The original is in the Gauß, Werke, Bd. 2, S. 178 . Hätte man +1, -1, √-1) nicht positiv, negative, imaginäre (oder gar um...

Why parallelogram area is |ad-bc|?

Here is my question. The area of parallelogram is the difference of these two rectangles (red rectangle - blue rectangle). This is not intuitive for me. If you also think it is not so intuitive, you might interested in my slides. I try to explain this for hight school students. Slides: A bit intuitive (for me) explanation of area of parallelogram (to my site, external link) .

Lx=d: SundayResearch

Search This Blog