Tuesday, July 28, 2015

Explain this Scenario in Jeapardy and some more thoughts

In the last post I had the following scenario:

Larry, Moe, and Curly are on Jeopardy.

Going into Final Jeopardy:

Larry has \$50,000, Moe has \$10,000, Curly has \$10,000

Larry bets \$29,999, Moe bets \$10,000, Curly bets \$10,000

These bets are ALL RATIONAL and ALL MATTER independent of what the category is. For example, these bets make sense whether the category is THE THREE STOOGES or CIRCUIT LOWER BOUNDS.

Explain why this is.

EXPLANATION: You were probably thinking of ordinary Jeopardy where the winner gets whatever he gets, and the losers take-home is based ONLY on their rank (2000 for second place, 1000 for first place). Hence Larry's bet seems risky since he may lose 29,999 and Moe and Curly's bets seem irrelevant (or barely relelvent- they both want to finish in second)

BUT- these are Larry, Moe, Curly, The Three Stooges. This is CELEBRITY JEOPARDY! The rules for money are different. First place gets MAX of what he wins, and 50,000. So Larry has NOTHING TO LOSE by betting 29,999.  Second and Third place BOTH get MAX of what they win and 10,000. So Moe and Curly have NOTHING TO LOSE by betting 10,000. (I suspect they do this because the money goes to a charity chosen by the celebrity).

SIDE NOTE: I saw Celebrity Jeopardy and wanted to verify the above before posting. So I looked on the web for the rules for Celebrity Jeopardy. THEY WERE NO WHERE TO BE FOUND! A friend of mine finally found a very brief you-tube clip of Penn Jillette wining  Celeb Jeopardy and a VERY BRIEF look at the final scores and how much money everyone actually got. Thats how I verified what I thought were the rules for celebrity jeopardy.

IF I am looking up a theorem in Recursive Ramsey theory and can't find it on the web I am NOT surprised at all since that would be somewhat obscure (9 times out of 10 when I look up something in Ramsey Theory it points to one of the Ramsey Theory Websites that I maintain. Usually is there!). But the rules for final Jeopardy -- I would think that is not so obscure. Rather surprised it was not on the web.

Monday, July 27, 2015

Explain this Scenario on Jeopardy

Ponder the following:

Larry, Moe, and Curly are on Jeopardy.

Going into Final Jeopardy:

Larry has \$50,000, Moe has \$10,000, Curly has \$10,000

Larry bets \$29,999, Moe bets \$10,000, Curly bets \$10,000

These bets are ALL RATIONAL and ALL MATTER independent of what the category is. For example, these bets make sense whether the category is THE THREE STOOGES or CIRCUIT LOWER BOUNDS.

Explain why this is.

I'll answer in my next post or in the comments of this one
depending on... not sure what it depends on.

Thursday, July 23, 2015

New Proof of the Isolation Lemma

The isolation lemma of Mulmuley, Vazirani and Vazirani says that if we take random weights for elements in a set system, with high probability there will be a unique set of minimum weight. Mulmuley et al. use the isolation lemma to randomly reduce matching to computing the determinant. The isolation lemma also gives an alternative proof to Valiant-Vazirani that show how to randomly reduce NP-complete problems to ones with a unique solution.

Noam Ta-Shma, an Israeli high school student (and son of Amnon), recently posted a new proof of the isolation lemma. The MVV proof is not particularly complicated but it does require feeling very comfortable with independent random variables. Ta-Shma's proof is a more straight-forward combinatorial argument.

Suppose you have a set system over a universe of n elements. Give each element i, a weight wi uniformly chosen between 1 and m. The weight of a set is the sum of the weights of the elements of that set. Ta-Shma shows that there is a unique minimum weighted set with probability at least (1-1/m)n, which beats out the bound of (1-n/m) given by MVV.

Here is a sketch of his proof: Suppose all the wi's had weights between 2 and m. Let S be the lexicographically minimal weight set given these weights. Consider the function φ(w), defined on weights with all the wi at least 2, as the following:
• φ(w)i = wi -1 if i is in S
• φ(w)i = wi if i is not in S
Note that S is the unique minimal set now in the weights φ(w)i. Moreover φ is 1-1 for we can recover w from φ(w) by taking the unique minimal weight set in φ(w) and adding one to the weight of each element in that set.

So we have the probability that random weights yield a unique minimum set is at least
|range(φ)|/mn = |domain(φ)|/mn = (m-1)n/mn = (1-1/m)n.

Read all the details in Ta-Shma's paper.

Tuesday, July 21, 2015

Hartley Rogers, Author of the first Textbook on Recursion Theory, passes away

Hartley Rogers Jr passed away on July 17, 2015 (last week Friday as I write this).He was 89 and passed peacefully.

For our community Rogers is probably best known for his textbook on Recursion Theory which I discuss below. He did many other things, for which I refer you to

His book was:

The theory of recursive functions and effective computability.

It was first published in 1967 but a paperback version came out in 1987.

It was probably the first textbook in recursion theory. It was fairly broad. Here are the chapter headings and some comments.
Recursive functions

Unsolvable problems (The first edition came out before Hilbert's tenth problem was solved),

Purpose: Summary,

Recursive invariants,

Recursive and recursively enumerable sets,

Reducibilities,

One-One Reducibilities; Many-one Reducibilities, (Maybe its just me but I can't imagine caring if the reduction is 1-1 or m-1.)

Truth-Table Reducibilities;simple sets, (``simple sets are not simple'' was a quote from Herbert Gelernter who taught me my first course in recursion theory.)

Turing Reducibilities; hypersimple sets,

Post's Problem; incomplete sets. (Posts problem was to find an r.e. set that is neither recursive nor Turing-complete. when I tell people there such a set they they often say `Oh, Like Ladner's Theorem.' Thats true but backwards. Its  still open to find a NATURAL set that is incomplete, though they prob don't exist and its hard to pin that down.)

The Recursion Theorem,

Recursively enumerable sets as a lattice,

Degrees of unsolvability,

The Arithmetic Hierarchy (Part 1),

The Arithmetic Hierarchy (Part 2),

The Analytic Hierarchy.

Looking over his book I notice the following

1) He thanks Noam Chomsky (a linguist) and Burton Dreben (A philosopher). I think we are more specialized now. Would it be surprising if a text in recursion theory written now thanked people who are not in math?

2) He thanks his typist. I think that people who write math books now type it themselves. I wonder if novelists also now type it themselves.

3) I think that Soare's book replaced it as THE book that young recursion theorists read. (Are there young recursion theorists?)  Soare's book is chiefly on r.e. degree theory, Rogers book is broader. When Rogers wrote his book much less was known (no 0'''-arguments, very little on random sets). It was possible to have most of what was known in one book. That would be hard now, though Odilfreddi book comes close. Note that Odilfreddi book is in two volumes with a third one to be finished... probably never.

One personal note- I had a course on Recursion theory taught by Herbert Gelernter at Stonybrook (my ugrad school) in the Fall of 1979. We covered the first six chapters of Rogers text. It was a great course from a great book taught by a great teacher and set me on the path to do work in recursion-theoretic complexity theory.

Thursday, July 16, 2015

Microsoft Faculty Summit

Last week I participated in my first Microsoft Faculty Summit, an annual soiree where Microsoft brings about a hundred faculty to Redmond to see the latest in Microsoft Research. I love these kinds of meetings because I enjoy getting the chance to talk to computer scientists across the broad spectrum of research. Unlike other field, CS hasn't had a true annual meeting since the 80's so it takes events like this to bring subareas together. "Unlike other fields" is an expression we say far too often in computer science.

This was the first summit since the closing of the Silicon Valley lab and the reorganization of MSR into NExT (New Experiences and Technologies) led by Peter Lee and MSR Labs led by Jeannette Wing. Labs focusing on long-term research while NExT tries to put research into Microsoft products. Peter gave the example of real-time translation into Skype already available for public preview. Everyone in MSR emphasized that Microsoft will remain committed to open long-term research and said the latest round of cuts (announced while the summit was happening) will not affect research.

HoloLens had the most excitement, a way to manipulate virtual three-dimensional images. Unfortunately the summit didn't have HoloLenses for us to try out but I did get a cool HoloLens T-shirt. While one expects the most interest in HoloLens for gaming, Microsoft emphasized the educational aspect. Microsoft has a call for proposals for research and education uses for HoloLens.

I didn't go to many of the parallel sessions, instead spending the time networking with colleagues old and new. I did really enjoy the research showcase which highlight many of the research projects. I tried out the Skype translator, failing a reverse Turing test because I thought I was talking to a computer but it was really a Spanish speaking human. My colleagues at MSR NYC were showing off their wisdom of the crowds. Microsoft is moving their defunct academic search directly into Bing and Cortana. I tried Binging myself on the prototype and it did indeed list my research papers but not my homepage and this blog. They said they'll fix that in future updates.

Monica Lam showed off her latest social messaging system Omlet to improve privacy by keeping data on the Omlet server for no longer than two weeks though I was more excited by their open API. Feel free to Omlet me.

While the meeting had its share of hype (quantum computers to solve world hunger), I really enjoyed the couple of days in Redmond. Despite the SVC closing, Microsoft is still one of the few companies that has labs focused on true basic research.

Monday, July 13, 2015

Is there an easier proof? A less messy proof?

Consider the following statement:

BEGIN STATEMENT:

For all a,b,c, the equations

x + y + z = a

x2 +y2 + z2 = b

x3 + y3 + z3 = c

has a unique solution (up to perms of x,y,z).

END STATEMENT

One can also look at this with k equations, k variables, and powers 1,2,...,k.

The STATEMENT is true. One can use Newton's  identities (see here) to obtain from the sums-of-powers all of the symmetric functions of x,y,z (uniquely). One can then form a polynomial which, in the k=3 case, is

W^3 -(x+y+z)W^2 + (xy+xz+yz)W - xyz = 0

whose roots are what we seek.

I want to prove an easier theorem in an easier way that avoids using Newton's identities. Here is what I want to prove:

Given those equations above (or the version with k-powers), and told that a,b,c are nonzero natural numbers, I want to prove that there is at most one natural-number solution for (x,y,z)  (OR for x1,...,xk in the k-power case).

Its hard to say `I want an easier proof' when the proof at hand really isn't that hard. And I don't want to say I want an `elementary' proof- I just want to avoid the messiness of Newton's identities. I doubt I can formalize what I want but, as Potter Stewart said, I'll know it when I see it.

Thursday, July 09, 2015

Will Our Understanding of Math Deteriorate Over Time?

Scientific American writes about rescuing the enormous theorem (classification of finite simple groups) before the proof vanishes. How can a proof vanish?

In mathematics and theoretical computer science, we read research papers primarily to find research questions to work on, or find techniques we can use to prove new theorems. What happens to a research area then when researchers go elsewhere?

In a response to a question about how can one contribute to mathematics, Bill Thurston notes that our knowledge of mathematics can deteriorate over time.
Mathematical understanding does not expand in a monotone direction. Our understanding frequently deteriorates as well. There are several obvious mechanisms of decay. The experts in a subject retire and die, or simply move on to other subjects and forget. Mathematics is commonly explained and recorded in symbolic and concrete forms that are easy to communicate, rather than in conceptual forms that are easy to understand once communicated. Translation in the direction conceptual -> concrete and symbolic is much easier than translation in the reverse direction, and symbolic forms often replaces the conceptual forms of understanding. And mathematical conventions and taken-for-granted knowledge change, so older texts may become hard to understand. In short, mathematics only exists in a living community of mathematicians that spreads understanding and breaths life into ideas both old and new.
Once a research area fills out, researchers tend to move on to new and different ideas. Much of the research in the theoretical CS community in the 50's, 60's and 70's have been lost to journal articles, now nicely digitized but rarely downloaded.

What will happen with complexity classes once people stop studying them? You already don't see that many recent papers on complexity classes, even in the Computational Complexity Conference. A victim of our own success and failures: We settled most of the easy questions and the rest are very hard.  As my generation retires, the classes may retire as well, outside of a couple of the biggies like P and NP. The old papers will still be out there, and you can always look up the classes in the zoo or on Wikipedia, but the understanding that goes with people studying these classes, and why we cared about them, may deteriorate just like computer programs that go unattended.

Sunday, July 05, 2015

Does Bob Deserve the lavish acknowledgement: A problem in Logic

Alice and Carol are real mathematicians.
Bob is an English major who does not know any mathematics.

(This story is based on a true incident.)

Alice writes a math paper. Carol reads it and offers corrections of style and grammar and how-to-say-things. She also helps simplify some of the proofs. She does not deserve a co-authorship but Alice does of course write in the acknowledgements

I would like to thank Carol for proofreading and for help with some of the proofs.

Bob points out that this is silly --- if she would like to thank Carol then do so. So Alice changes it to

I thank Carol for proofreading and for help with some of the proofs.

Even though Bob does not understand the math he begins reading the paper. He finds a few grammar mistakes, some points of style, and even a math mistake:

BOB: Alice, this sentence mentions A1 and A2, is A1 the steak sauce?

ALICE:  Its A sub 1 and no it is not the steak sauce.

BOB: But later in the sentence there is a reference to A? Maybe its implicit what A is and I don't get it since I don't know the math, but it does look funny.

ALICE: Well pierce my ears and call be drafty! You're right! It should be A1, A2, and A_1 ∩ A_2.

SO, in the end Bob DID proofread the paper and DID help. Alice wants to include him in the acknowledgements. She modifies the ack to

I thank Bob and Carol for proofreading and help with some of the proofs.

Is that correct? Bob just did proofreading, and Carol did proofreading AND helped with some proofs. In logical terms

If B did X and C did X and Y then

B AND C did X AND  Y

does seem correct.

But is also seems misleading. Alice could separate it out:

I thank Carol for proofreading and help with some of the proofs.
I thank Bob and Carol for proofreading.

Thats more accurate but also more cumbersome.

But my real question is, is the I THANK BOB AND CAROL... statement correct or incorrect? In logic correct, in English, perhaps not. We could ask Bob who is an English major and maybe get a paper out of it which Carol can proofread!

Thursday, July 02, 2015

Goodbye SIGACT and CRA

Tuesday I served my last day on two organizations, the ACM SIGACT Executive Committee and the CRA Board of Directors.

I spent ten years on the SIGACT (Special Interest Group on Algorithms and Computation Theory) EC, four years as vice-chair, three years as chair and three years as ex-chair, admittedly not so active those last three years. SIGACT is the main US academic organization for theoretical computer science and organizes STOC as its flagship conference. I tried to do big things, managed a few smaller things (ToCT, a few more accepted papers in STOC, poster sessions, workshops, moving Knuth and Distinguished Service to annual awards, an award for best student presentation, a tiered PC), some of them stuck and some of them didn't. Glad to see a new movement to try big changes to meet the main challenge that no conference, including STOC, really brings the theory community together anymore. As Michael Mitzenmacher becomes chair and Paul Beame takes my place as ex-chair, I wish them them and SIGACT well moving forward.

The Computing Research Association's main efforts promotes computing research to industry and government and increasing the diversity in computing research. It's a well-run organization and we can thank them particularly for helping improve the funding situation for computing in difficult financial times. The CRA occasionally puts out best practices memos like a recent one recommending quality over quantity for hiring and promotion. Serving on the board, I most enjoyed interacting with computer scientists from across the entire field, instead of just hanging with theorists at the usual conferences and workshops.

One advantage of leaving these committees: I can now kibbitz more freely on the theory community and computing in general. Should be fun.