"Logic will reliably indicate what you can't do, for the rest ..." (Jad Nohra)

A cross-product (determinant) saved my life, or did it?

Your friend has been kidnapped by evil perfectionists, they put him in the middle of a square room, with two opposite walls painted one black one blue, and the other two painted white, there is a door at each white wall, one leads to instant death by vaporization and the other to freedom. In the middle of the ceiling there is a tiny circular hole from which your friend can receive your voice and send his and nothing else.
He is facing a black wall, and if he does not escape the room within one minute he will be vaporized. Everything that can be sensed by a human is perfectly symmetrical in that room. Your vulgar friend does not know his left from his right, but you know that the door to his right leads to freedom.
What is a better use of your time? Trying to lead your friend to the door, or going for a cup of coffee?

We are in the future, 10 years later. We have established contact with a large amount of different intelligent alien species, and you even befriended an alien. To celebrate the vaporization of your last friend, evil hopeless perfectionists kidnap your alien friend, and put him in the same situation. Everything that can be sensed by this alien is perfectly symmetrical in that room.
At this point I need to tell you a bit about him: his species is Platonicus Solidus, he is a perfect sphere. He has a circular bottom on which he can bounce or rotate, and a diametrically opposed top from which he can hear, and under which his perfectly spherical brain resides. His sight is handled by 4 perfectly spherical and identical eyes, arranged symmetrically along his equator, he can never tell them apart.
However, your friend can actually feel the difference between clockwise and counter-clockwise rotation! So the kidnappers think you have better chances.
You know that the right door is to your right if you were in there facing the black wall.
Is it time for another coffee?

Releasing some old code and music.

Here is the source code for the old XNA Rendering Framework / Quake3 Renderer:
http://jadnohra.net/release/XnaFramework1-Quake3Renderer.zip

It might be useful for somebody trying to write a Quake3 level loader.

And I also stumbled upon this old strange piece of music that I made for Lena at the time where I still had time to touch the guitar:
http://jadnohra.net/release/DeadGuitars/JadNohra_ConcertoForElectricGuitar_DayOfBirth_MOV04530.MPG

Not good

0x15230600 3f800000 00000000 00000000 00000000 ..€?............
0x15230610 00000000 3f800000 00000000 00000000 ......€?........
0x15230620 00000000 00000000 3f800000 00000000 ..........€?....
0x15230630 c0499999 3fc3d70a 00000000 00000000

0x41140600 3f800000 00000000 00000000 00000000 ?€..............
0x41140610 00000000 3f800000 00000000 00000000 ....?€..........
0x41140620 00000000 00000000 3f800000 00000000 ........?€......
0x41140630 c0499998 3fc3d70a 00000000 00000000

Rotation is so much more interesting than translation, (Level up)

Randomness works as expected.

http://www.rpscontest.com/authorSearch?name=Jad+Nohra
If only I could find the right prime for each opponent hahahaha, or the right place to start in sqrt(2).

Of course genius Tom is smarter:
http://www.rpscontest.com/entry/110017

Forcing yourself to do multiple versions of the same proof is like body building.

Prediction about my future child's diary.

"Dear diary.

Monday, dad said we would go buy new tennis shoes if I find the one number that multiplied by itself, gives 9, by trial and error using multiplication, I found it very fast and I found nice shoes as well.

Tuesday, he said we would go buy a new chess board if I would do the same for 102.2121, it was more difficult but the result was the month and day of my birth, I liked that.

Today he must be going crazy, he said I can celebrate my birthday every week! if I do the same for 2, it took me all day and I am at 1.41421356237309504880168872420969807856967187537694807317667973799073247846210703885038753432764157273501384623091229702492483605585073721264412149709993583141322266592750559275579995050115278206057147010955997160597027453459686201472851741864088919860955232923048430871432145083976 but I must be really really close because 76 is the year my mom was born"

Book of Proof.

Tom had the brilliant idea of not biting off too much at once with real analysis and studying pure proof techniques. He also found a very good book for it, it is even free. http://www.people.vcu.edu/~rhammack/BookOfProof/index.html.

We like it because it is geared at exactly our goal and requires little to no prerequisites.

We have been working on it in the past months quite slowly because of some personal things that needed attention, but now I am back and we are at Chapter 5.

It has not been a very difficult book for now, but it has been perfect at showing us the edge of how we currently think and how to extend it, formalized proof 'techniques' (which does not replace the need for or ), along with confidence in formal proof writing.

The book is not to be confused with the famous 'Proofs from the Book' ! we definitely do not have what it takes to tackle that one yet, but if at some point we do, we will see it as success of our project.

More good news: We have somebody (a colleague Technical Artist) who decided to join us and has been catching up starting at week 1. Unfortunately, we have not been commenting on his insightful posts, but that is the price of starting late :). We do have verbal discussions at work though...

I conclude with a Frankenstein of a proof I made, which has a much more elegant alternative found by Tom. It is a nice example of two different ways of proving the same thing, how the use of properties is often crucial to write elegant proofs, how I am using my 'debugging the truth' technique, how to be patient, how not assume that if you cannot see the path right away you will not be able to find it at all, and how you can learn from failed proofs instead of throwing the towel.

http://jadnohra.net/release/math/book_of_proof/ex_4_23.pdf

https://sites.google.com/site/77neuronsprojectperelman/weeks/week-23

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Epsilon in $

"In the aluminum can industry, the thickness of the top of the pop-top cans has some physical limitations. It must be (say) not be thicker than 0.4mm, or else the poptop mechanism

may not work (many of us knows this from first hand experience). It must not be thinner than 0.3mm, or else the internal pressure may cause spontaneous explosion. Hence, we might tolerance this thickness as 0.35 ± 0.05mm. Now, if manufacturing processes were more reliable, and our ability to assess tolerance were more accurate, we might be able to tolerance this thickness as 0.32 ± 0.02mm. Such a change would save the aluminum can industry multi-millions of dollars in material cost each year".

"On 4 June 1996, the maiden flight of the 8 Ariane 5 launcher in French Guiana ended in self-destruction. About 40 seconds after initiation of the flight sequence, at an altitude of about 3700 m, the launcher veered off its flight path, broke up and exploded. A report from the Inquiry Board located the critical events: “At approximately 30 seconds after lift-off, the computer within the back-up inertial reference system, which was working on stand-by for guidance and attitude control, became inoperative. This was caused by an internal variable related to the horizontal velocity of the launcher exceeding a limit which existed in the software

of this computer. Approximately 0.05 seconds later the active inertial reference system, identical to the back-up system in hardware and software, failed for the same reason. Since the back-up inertial system was already inoperative, correct guidance and attitude information could no longer be obtained and loss of the mission was inevitable.”

The software error began with an overflow problem: “The internal SRI software exception was caused during execution of a data conversion from 64-bit floating point to 16-bit signed integer value. The floating point number which was converted had a value greater than what could be represented by a 16-bit signed integer. This resulted in an Operand Error. The data conversion instructions (in Ada code) were not protected from causing an Operand Error, although other conversions of comparable variables in the same place in the code were protected.”

Spinozian Calculus.

http://www.yesselman.com/index.htm#Intro

Epsilon-Delta level up.

Me and Tom had a really good understanding of limits and continuity already, much better than we ever had before starting this project, but the FTC pushed as again the limits of our models, so we went back digging and getting an even deeper understanding.

Here is a part of my newest conclusions, as usual the full discussion is at: https://sites.google.com/site/77neuronsprojectperelman/weeks/week-19---5-6-proofs-ftc1-2

• Many seem to agree that the epsilon-delta definitions are annoying, This can be soon both at Karl's calculus page or on mathcs.org
• "

  Does that delta-epsilon method that we have been through a bunch of times now seem like a pain in the butt? Mathematicians are, by their nature, a lazy lot. If they can get away with doing some pain-in-the-butt operation just once and thereby come up with some easy and useful rule, then that's what they'll do. And once they know the rule to be true, they'll use it every time instead of the pain-in-the-butt method. Not only does the rule make life easier, but without such rules, mathematics would be so thick with undergrowth as to make it virtually impossible to understand."

• "This, like many epsilon-delta definitions and arguments, is not easy to understand."

• The fact that infinitesimal calculus was heavily supported by Newton and Leibniz, tells me again, that the classical definition of limits simply does feel annoying and people tried to find 'better' ways.
• At the same time, based on Bishop, they are common sense, so there must be a way to understand why they are the best way to describe what they do describe.

I went through Karl's Calculus pages again, the number system and limits parts. I am starting to live revising things even more. Things become clearer every time I read them, even if it is the same text.

I had a slight change of mental model after I did this, I will try to describe it.

Without thinking strictly about functions, limits are interesting places that really are related to a computation that is in seemingly impossible at infinite precision, at least at first sight.

They involve interesting places involving infinities, like the integral being a sum of an infinite large count of infinitely small numbers, or in a sequence of converging quantities, where we know we can get as close as we wish to some quantity yet to be found, or in derivatives, where we want to know if we can get as close as we like to some quantity to be found, starting with the ratio of 2 infinitely small quantities.

All interesting places.

Another point is that limits are about a relationship, the relationship between a domain (input), a range (output) and a function (a computational algorithm). I am finding it useful to visualize each of these separately instead of as a curve. The idea is that is that you take a piece of the domain, which is continuous by the very fact that we are dealing with reals and have a density (to be discussed!), and then taking at the piece of the range that the algorithm produces, again luckily, the reals make it even possible for that piece to be 'continuous' because the reals are closed under the operators found in the function, and check that piece of range out.

Is it connected just like the piece of domain is? is it not?

This is related to one other important point, it is not good to think of this as walking along the domain in some direction and looking at the range, specially not when we talking about limits around a specific point.

When we do this, the focus is on the point, so we start from that point in the domain and expand out, in the range, we start at the point's output and expand out, it is a subtle but important difference, specially that it made me realize how mixed together the multiple kinds of continuity in my mind. I always used to think that a function being continuous in calculus means continuous at every point, and whenever I was confronted with having to use this, I started thinking about some kind of induction logic to show that continuous at every point made all the points somehow connected. But there is also uniformly continuous, continuous at every point but not uniformly continuous, etc... "But first, let me answer a few questions that curiosity may be stuffing into your head at this very moment. In the example of u(x) we saw a function that was continuous everywhere except at one point. Is there a function that is continuous everywhere except at several points? Yes. Is there one that is continuous everywhere except at infinitely many isolated points? Yes. Is there one that is continuous nowhere at all? Yes. Is there one that is continuous only at a single point? Yes. Is there a function that is continuous everywhere yet cannot be graphed? Yes. And later on I shall give you examples of all of these. Click here if you want to skip ahead and see this optional material right now. Or you can continue reading and you will get to it eventually."

I have done some introspection and I came to some conclusions about what made me uncomfortable about epsilon-delta definitions.

Although I really did understand them they still felt strange in the sense that one would think that there must be a better, nicer, more usable way to express this, something that can be manipulated easily like algebra.

But after giving this some deep thought I came out even more convinced of Bishop's argument that it is common sense,

1. They are a relationship between domain and range
2. The relationship is TOTALLY dependent on the function, the algorithm that maps domain to range

This means, there is no general lazy way of having limits that solve themselves using mechanical manipulation, because it DEPENDS on the operator, this made me coin one term that I have been noticing the more I went into theory be it math, computer science, solving problems at work ... limits will always be in the category: among other categories.

The problem can be reduced to having to FIND a relationship between epsilon and delta that satisfies some constraints, or FIND a counter example. Like all other 'inverse' problems, where we know the goal but the path is still to be found, it is also in the category: .
Those are 2 uncomfortable categories, they do not allow for laziness, impatience, or lack of intuition and very solid understanding. It is a game...

But once this had crystallized in my mind like this, it suddenly began to feel much more comfortable.

Also, thinking about it like this, separating domain and range, looking at them separately, and looking at the problem in terms of sequence convergence for one point, started to convince that the epsilon-delta is the best definition because it does say in math exactly what we are saying.

I still have to wrap my investigate EVT and MVT and see how they are related to point continuity, uniform continuity, continuity in calculus. This will be the last piece of a level up.

I now see MVT and EVT as THE calculus formal tools that stem from the essence of epsilon-delta and can luckily be used instead of epsilon-delta in some cases to alleviate the need for hairy statements.

It is like this: you can build a basic airplane from pieces of metal and fuel, but if you are planning a war campaign you do not want to be planning on the level of detail of pieces of metal and fuel, you just start with airplanes, otherwize, while still possible, it becomes very hard very fast, ah, theorems are great building blocks, reducing everything to axioms will trash the caches of our tiny brains very fast. "

Not only does the rule make life easier, but without such rules, mathematics would be so thick with undergrowth as to make it virtually impossible to understand.""

Non-elementary functions are to elementary functions what irrationals are to rationals. (Jad Nohra).

Bigfoot update: Skeleton semantics, Footplant WIP.

I took some time today to work on Bigfoot (my animation research testbed) a bit.
The first thing I added was not animation related, my UI library did not support multi-sampling when rendering 3D to textures, now it does, and all my skeletons look happier.

On the animation side, I added some skeleton semantic detection code. Before, the skeletons were only analyzed for branches, chains of bones with one child only. Now it also find symmetries between branches, in the beginning of the video you can see how it detects that the left and right limbs are symmetrical. The next step is to give it some human skeleton knowledge, so that it automatically figures out what is a head, a foot, a leg, etc... The point of this is that it would enable running the code on large mocap databases without the need for human annotation for purposes like machine learning.

The other new feature which is still very much work in progress is footplant detection. While seemingly innocent, it can be quite tricky to get this right. Mocap is noisy and I also want to support the more general case of 'support contact', where for an animation of an athlete hanging on a bar per example, the contact points with the bar would be detected, or for an unrealistic animation of a martial arts kick after taking a few steps on a vertical wall, the steps on the wall would be registered as well. This needs a different technique than simply foot height. I am researching this slowly when I find myself needing a break from Mathematics and want to do something instantly gratifying.

In the video, green spheres are generated when there is a local minimum in joint height, blue ones when there is a local minimum in joint velocity and white for both.

You can see lots of them firing during footplants. I tried to filter the signals and that did improve the detection, but this is only the beginning, it needs to get much better.

"If Calculus was c, Analysis would be assembly, Set Theory would be machine code, and Logic would be transistors." (Jad Nohra and Tom Lahore)

1 = 2, Q.E.D

Tom and me came up with this nice contraption while analyzing calculus proofs, can you figure out what is wrong with it? you can reply on mathbin at: http://mathbin.net/59026

Is this 'limit replacement' property trivially true?

I have lately been bumping calculus proofs where this property of limits would be really useful, but I am not sure it is true even though it seems trivially true. I have just formulated it but not tried to prove it yet, I will try using the formal definition of limits. Comments welcome.

Microscopically intuitive FTC#1, take 2.

Last week, I added a small paragraph at the bottom of my Fundamental Theorem of Calculus proof attempt, trying to cast an intuitive view on the theorem,

based on my observation that, when focusing on one tiny interval, proving the FTC and understanding it is intuitive.

The paragraph was rushed and did not contain a much needed figure, therefore when I showed it to Tom he could not make sense out of it although I thought it was a really nice insight.

While analyzing some FTC proofs, I became even more aware of how useful this intuition was.

I also become aware that some proofs simply require one to work out each detail of their intuition rigorously and patiently and not much more.

I decided to take the time to polish my insight, and see if I can manage to explain it better.

One thing I realized is that it takes it quite an amount text to explain even the simplest ideas if ones wants to do it right...

Here it is: http://jadnohra.net/release/math/ftc1_intuition_micro.pdf

Limit over an interval

We are analyzing several FTC proofs to gain some insights. For now it seems all of them need analysis to be stated with enough detail to be convincing.

In this proof, I stumbled upon an assumption that can be reduced to claiming that this statement is true:

As usual, this is intuitively very true, the interval vanishes, leaving the 'sup' to act on only 'one point' if f is continuous. But that is no proof.

I have tried to detail this a bit more to see if I can prove it, the main idea behind my proof is: Courage.
I have found courage to be an essential component across many proofs and bold inventions in mathematics.
I am not sure how good it is, it feels pretty convincing, but there are 2 spots where it needs more detail, and I suspect that for these spots, there is an inescapable need for analysis (luckily we will be tackling that in the foreseeable future).

.

Yet another 'intuitive' concept to use in my PROOFS? what is this? a pudding recipe? (Jad Nohra)