Skip to main content

Intermission 1 (lambda calculus)

I have a Japanese version of this page. There was a good question on my last article. ``What happen if the vending machine (a function) is broken?''

First of all, we need to define what broken means. Some of you would say, ``Broken is broken, what else?'' But, this answer does not make any sense for mathematicians. Are there no common sense in the head of mathematician? Maybe, yes. But, there is a reason.

I am a Sunday mathematician/programmer. Mainly I program a code to solve some of my problems. To tell my computer to solve my problem, I need to interpret my problem to a code which my computer can execute/understand. Many of mathematics formulation is really formulated, which means you do not need to understand what it is, they are just a procedure. Then my computer can execute to solve my problem. I formulate some problem since after that is done, I do not need to think about that. Rest of the problem is solved automatically. This is fun for me. ``Computer, search some information. Computer, find the shortest path from my home to the station. Computer, find the cheapest ticket under this condition...'' All these things must be translated to a code which my computer can understand. ``Broken is broken'' is not enough for the computer. Since computers are so stupid so far.

For example, Broken could mean 1. when you input something, but nothing comes out, 2. when you input anything, the output is always the same, or 3. when you input something, the output seems totally random. Which is the broken means for you? None of them? Current usual computer can not guess, we need to tell that.

Also, ``broken'' has subjective meaning. There are chips which have build-in self destruction mechanism. For example, some kind of decryption chips. These chips contain a secret encryption key, so some malicious people want to read it. When the chip detects such activity, it breaks itself. Some of the credit card chips and DVD copy detection chips have this function.

When you can not read the information, usually it means ``broken.'' But the designer of these chips designed to do that. If someone can still read the secret information, it is broken for the designer. Therefore, ``broken'' is subjective meaning. When someone's credit card is stolen, the owner usually does not want to his/her card available anymore. If the chip does not self destructed by the malicious one's attack, then the owner may sue the designer, ``The chip was not broken, because it was broken. If it is not broken, it should have broken itself.'' A human can understand this means, but, it is difficult for current machines.

Lambda calculus thinks about all kind of functions. Therefore, such ``broken'' function (whatever it means) must be described. If lambda calculus can not describe some of the functions, that is the limit of this calculus. But, a person must define what is the broken means if he/she want to describe it in lambda calculus. Mathematician is a such a lazy people, but they are also perfectionist. The art of mathematics is how to reach the ``perfect laziness.'' Therfore, all kinds of functions are of course considered. In the a few thousand years of mathematics history, one era is ended when the people found out the perfectness of mathematics system or limit of mathematics system. But this story is too large here and I would like to concentrate only at the some aspect of the lambda calculus. Although, I would like to mention about that if I could.

Comments

Popular posts from this blog

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) . 

Geometric Multiplicity: eignvectors (2)

If eigenvectors of a matrix A are independent, it is a happy property. Because the matrix A can be diagonalized with a matrix S that column vectors are eigenvectors of A . For example, Why this is a happy property of A? Because I can find A's power easily. A^{10} is not a big deal. Because Λ is a diagonal matrix and power of a diagonal matrix is quite simple. A^{10} = SΛ^{10} S^{-1} Then, why if I want to compute power of A ? That is the same reason to find eigenvectors. Eigenvectors are a basis of a matrix. A matrix can be represented by a single scalar. I repeat this again. This is the happy point, a matrix becomes a scalar. What can be simpler than a scalar value. But, this is only possible when the matrix S's columns are independent. Because S^{-1} must be exist. Now I come back to my first question. Is the λ's multiplicity related with the number of eigenvectors? This time I found this has the name. Geometric multiplicity (GM): the number of in...

Tezuka Osamu's Black Jack, "Shrinking"

I like several novel authors. My first favorite author is probably Teduka, Osamu. I still love him. The list grows by adding Hoshi, Shinichi, Agatha Christie, Hermann Hesse, and so forth. My first favorite article of Tezuka was Atom as most of the (boy's) Tezuka fans did. But my favorite is Black Jack. I try to summarize one story, it is still quite vivid in my memory. I first read this story when I was 13 - 15 years old. I re-read it at least several times since Black Jack is composed of many short episodes. The title should be "ちぢむ (SHRINKING)" or it might be "縮む(Shrinking)". (It is not so convenient to translate this to English, since English does not have a system to say the exact same word in several ways. So I just simulate it with capital letters.) Black Jack is a genius surgeon, but he does not have the license. In short, his medical activity is illegal. His skill is top level in the world, but, the fee is also out-of-law expensive. In the story ...