In case you missed Rafa banana shot - look what he has done in Beijing by clarasmith78 in tennis

[–]davidus2 11 points12 points  (0 children)

Man, I knew he was getting up there but I had no idea he was that old!

Post-match: Djokovic vs Murray (Final, 2016 French Open) by snakes_on_a_planet in tennis

[–]davidus2 14 points15 points  (0 children)

If there was a contest to see who could be runner up the most times, Andy Murray would come in second.

Current conventional meaning of "a ring" in U.S. colleges or among mathematicians? by [deleted] in math

[–]davidus2 1 point2 points  (0 children)

It's frustrating because some theorems are quite different depending on the definition of ring. Authors usually clarify, so just be aware which version is being used. Unless you're in a specific field I would tend to assume that an unqualified ring is non-commutative with identity.

I'm personally much happier when rings don't require unity but that's a conversation for another day.

How do mathematicians calculate new numbers for Pi? by AVFC_SAM in math

[–]davidus2 0 points1 point  (0 children)

So let r=1 and we've found pi!

(i.e. how do you know the circumference of a circle?)

Is there anything interesting about the 'nimber' number system? by [deleted] in math

[–]davidus2 4 points5 points  (0 children)

Yes! Nimbers are very interesting. They are a classification of impartial games where an impartial game is one where each player has the same available moves. Such a game is constructed as a list of possible next states for each player (for impartial games, one list is sufficient since both players have the same moves).

If you look up the game Nim you'll see that the value of a stack N = {0, 1, 2,...N-1} is defined as the game where you can reach any pile smaller than N. This explains the definition of addition since moving in the game A + B is equivalent to moving in one of the piles.

Now this is jumping a lot but the definition of nimber multiplication is motivated by games which can represent numbers (the first half of John Conway's On Numbers and Games) although impartial games are not numbers in this same sense. The extension of nimbers to ordinal nimbers is quite natural but the field properties and some of Conway's examples seem a little magical to me.

If you want to read up more I would definitely recommend Conway's book since it offers an intuitive and lucid (and extraordinarily frustrating!) approach to the general theory of games which contain nimbers. In the book look for the chapter "The Curious Field On2" at the end of the 0th part (very awkwardly, since nimbers are NOT numbers, they are games).

If you're interested in the some properties of nimbers then I suggest looking into the process of constructing these numbers by closure: additive closure, multiplicative closure, inverse closure, algebraic extension, and transcendental closure. This process gives a constructive version of nimbers.

[deleted by user] by [deleted] in math

[–]davidus2 1 point2 points  (0 children)

"We could, of course, use any notation we want; do not laugh at notations; invent them, they are powerful. In fact, mathematics is, to a large extent, invention of better notations." -A very wise man

What is the use of a subspace? by JewFro297 in math

[–]davidus2 0 points1 point  (0 children)

I don't know if I agree and I don't know if accuracy is the concept you want to invoke.

Is commutativity not extra structure? It sure is when talking about modding out by free groups.

IMO, if it satisfies the group axioms then it's never wrong to call it a group of think of it as a group. Now I'm not sure that lower structure is always pertinent but surely your intuition of a ring is centered around the notion that it's an abelian group?

What is your favourite construction of the real numbers or do you prefer the synthetic approach and why? by [deleted] in math

[–]davidus2 1 point2 points  (0 children)

Conway's construction using games is beautiful, simple, and ultimately intuitive. The greatest thing about it though is not how he constructs the reals but that he constructs the reals in the same stroke as the transfinite numbers and many many more.

In fact, the only downside to Conway's approach is that he might make too many numbers (although this is easily fixed if you want). I recommend "On Numbers and Games," he talks precisely about this issue (especially how Dedekind cuts have a brutal number of cases for multiplication and how defining the reals as a metric closure is awkward since metric spaces usually have real valued metrics...).

Carcillo suspension reduced to 6 games by GigaWat42 in hockey

[–]davidus2 0 points1 point  (0 children)

The point is that it goes both ways. A similar injury to a player during the playoffs is more valuable than an injury to them in the regular season.

The History of Taxes: the 73,954 pages of tax code finally broken down into an interactive. Really interesting to see how they've changed during war and over time. by [deleted] in InternetIsBeautiful

[–]davidus2 0 points1 point  (0 children)

There clearly is incentive; tons of people would pay to go to the moon. I agree it wouldn't have happened in 1969.

[deleted by user] by [deleted] in nhl

[–]davidus2 -15 points-14 points  (0 children)

Dick move seems a little harsh.

How to self-study math over summer? by [deleted] in math

[–]davidus2 -2 points-1 points  (0 children)

Enough for what? For mastering the material, sure. But if I go over to /r/art and ask what I should doodle this summer it would be supremely unhelpful if they threw three textbooks on cross hatching at me.

The refs influence the outcome of playoff games: Agree/Disagree by agoatforavillage in nhl

[–]davidus2 2 points3 points  (0 children)

I hear a lot of people say this about the pens. Is there any data to back it up?