## Thursday, May 29, 2014

### Forgotten but not Lost in a Mapless World

Massimo Vignelli passed away on Tuesday, a visionary designer known for many things in particularly the
1970s NYC Subway Map. I used to pour over this map as a kid, finding the shortest route from my father's apartment on the upper east side to such exotic places like Coney Island. The subway map was not at all close to scale, central park certainly is not more wide than tall, but that didn't matter to me. The map did a great job showing how all the lines interconnected and that's all I needed.

I had a great skill in my younger days getting places using maps. I abhorred getting directions or following people--just tell me where you want me to be and I'll find it with a good (or at least topologically correct) map. If you make a mistake with directions you get hopelessly lost. If you take a wrong turn, a map is self-correcting.

My daughter was surprised to hear I used to carry maps in my car. Now I just use Google Maps to show me the way. I completely lost my map finding skills and often my sense of direction. Last week I ate at a restaurant managed by a relative in San Antonio. I couldn't really tell you where in San Antonio it was, Google Maps just took me on a series of highways to get there and then a series of highways to get to my hotel near the airport afterwards.

In the future when we just get into our steering wheel-less self-driving cars and enter our destination on a smartphone, we may all lose our sense of direction. Just like we no longer remember phone numbers, we just type in our friend's name to be taken to their place of residence. Location may not matter any more, we'll leave it all to the machines.

## Monday, May 26, 2014

### Review of People, Problems and Proofs By Lipton and Regan

(A version of this either already has or well appear in SIGACT NEWS book rev column.)

A review of the blog-book  PEOPLE, PROBLEMS, AND PROOFS by Richard Lipton and Ken Regan in the form of a blog.

FIRST POST: OVERVIEW OF PEOPLE, PROBLEMS, PROOFS.

This is the second book to be written based on the blog GODEL'S LOST LETTER AND P=NP.  The first one was THE P=NP QUESTION AND GODEL"S LOST LETTER. Both books are available on amazon: here and here.

When I read the GLL blog I often read it, get interested, but then something comes up so I can't finish it.THE BLOG WILL GET READ... TOMORROW! BET YOUR BOTTOM DOLLAR THAT TOMORROW, I WILL READ! Yet having it in book form it seems easier to read. It seems that the chapters in this book are shorter than the blog. If so that's a bit odd since one would think the book version could afford to be longer.

The upshot is positive--- I read the entire book (rare for a math book) understood most of it (rarer still) and am inspired to read more about the topics he introduced, and try to prove things for myself.  I"LL PROVE THE THER-EMS TOMORROW! BET YOUR BOTTOM DOLLAR THAT TOMORROW, I WILL PROVE.

April 20, 2014. Second Post on People, Problems, and Proofs

SECOND POST: ARE LIPTON AND REGAN REALLY THAT NICE?

Richard Lipton and Ken Regan are nice people.  Or their blog-selves are nice people. Most chapters have as its title a person and a subtitle that is more about the content. The link between the person ]and the content varies.  His descriptions of the people in the title of the chapters is always quite positive.

In Chapter 34, titled {Sam Buss: Bounded Logic}, Lipton talks about two courses he had in logic. In one the professor was often confused.  The other course was taught in a unmotivated way. He said they were both great courses.  That's being too nice.

The chapter itself was also nice. It involved ways to write quantifiers and refers to a result (which I will look up tomorrow) about inexpressibility.

Chapter 38 is about definitions. The title is
ALFONSO BEDOYA: DEFINITIONS, DEFINITIONS, and DEFINITIONS.
You may be wondering WHO IS THAT?. If you are under 35 you've probably already Googled it on some device you carry around and found out that he was the character Gold Hat in THE TREASURE OF SIERRA MADRE who uttered the famous line:

Badges? We ain't got no badges. We don't need no badges I don't have to show you any stinking badges!'' (see here for the original and see here for a satire from the classic movie UHF).

(Number 36 in the American Film Institutes 100 best movie quotes. The version from Sierra Madre, NOT the version from UHF, alas.)

Their point is that you don't need definitions--- they can always be removed. I thought they would say:

Definitions? We ain't got no definitions. We don't need no definitions.  I don't have to show you any stinking definitions!

But they cleaned it up (I didn't even know it was dirty!) to

Definitions, definitions, we don't need no definitions.

I'm surprised they didn't also remove the double negative, in case children are reading, to obtain

Definitions, definitions, we don't need any definitions.

The chapter itself was nice. It was about what makes a nice definition, and had some nice history. It was material I already knew but nice to have it all laid out.

TOWN FALCONER: You forgot to mention the one time they really were nice to a fault. They were nicer to that  guy who rudely wasted their time with a false proof that P NE NP.

GLACIAL WARMISH: Gee Town, if we ever turned our blog into a book nobody would accuse you of being to nice.  Anyway, they wisely spend Chapter One, THE CLAIMANT, THE READERS, AND THE CROWD, NOT replicating their blog, but telling the whole story from start to finish.  This is really good since now that the end is known its good to see how it all began. However, Town,  you are right, Lipton and Regan do not have any unkind words about him at all. Not even a tepid HE SHOULD AT SOME POINT HAVE MADE A FORMAL RETRACTION.

KEN REGAN: Too nice! How nice of you to say! However, note that the first paragraph of Section 1.12 of Chapter One I do note that Deolalikar has not addressed the issues raised.  So there!

SONATA CONSORT: Ken, you call that not-being-nice? You use words like Unfortunate'' and phrases like  we glean that (the revised version) did not increase appreciably in content''. Only nice people write like that. If I had spend a month pouring over an obviously flawed paper I would have written REST OF THIS COMMENT DELETED BY THE MODERATOR

ONE-CAT TREE: The chapter was more about crowd sourcing math than about the proof itself. This is an interesting topic; however, I think Terry Tao's polymath problems are a better and more productive example. And I also think that Lipton-Regan are too nice to say they disagree with me.

H.K. DONNUT: Wow, it sounds like Chapter One is awesome. Would you say it's worth the price of the book?

BILL G: Well...  I got my copy for free.  However, yes, Chapter 1 was, as the kids say, jawesome!

NOT PORN: I find your posts very nice.  For something even nicer click HERE for what I promise is NOT a porn site. At least not in most states.

THIRD  POST:  FOURTEEN LIGHT CHAPTERS

Not every post can be about an interesting piece of mathematics.  It would just be too hard (though Terry Tao seems to manage it). And in fact Lipton-Regan do not attempt this. Of the 63 chapters in the book, 14 of them are more ABOUT MATH then have hard math in them.  Things like how to guess what a result will be, how to try to prove it, the importance of a good notation, how to write up a result. These chapters were light reading but still informative.

COLBERT NATION: HEY, it can either be light reading OR informative, but it can't be both. We're at war here, pick a side!

BILL G: Here is an example. Chapter 2, titled KENNETH IVERSON: NOTATION AND THINKING didn't have any real math in it but it did tell me the following:

Descartes is the first person to use x^4 instead of xxxx.

Euler is the first person to use the Sigma for for summation and also the first one to use the notation f(x) for a function.

There is some debate about whether pi was the right number to since 2pi come up more often.

ALMA RHO-GRANT: Hey, YOU blogged on the pi thing yourself. So that can't be news to you.

BILL G: Yeah, but I FORGOT! As I was reading it I thought it was a neat issue to raise BEFORE I saw that I raised it. Awkward! More to the point--- this book is good at reminding you of things you once knew.

FOURTH  POST: FORTY NINE HEAVY CHAPTERS

If there are 63 chapters and 14 are light then 49 must be heavy. Actually the world is not quite so binary. However, there are 49 chapters that have math in them, much of it new and interesting. Since blogs are themselves summaries if I summarized all of them we may end up with some Quantum effects (Chapter 63---Charles Bennett: Quantum Protocols). Hence I summarize just a few.

Chapter 37 is titled THOMAS JECH: THE AXIOM OF CHOICE. Recall the usual axiom of choice:

Let I be a set (it could be of any cardinality). Assume that for every i in I there is a set X_i. There exists a function f (a choice function) from I to bigcup_{i in I} X_i such that f(i) in A_i. }

Look at the following restrictions of this. Let C_n be the following statement:

Let I be a set (it could be of any cardinality). Assume that for every i in I there is a set X_i such that |X_i|=n. There exists a function f (a choice function) from I to bigcup_{i in I} X_i such that f(i) in A_i.

For which n,m does C_n imply C_m? This chapter gives a clear statement of when this is true and gives some proofs of the easy direction (showing that C_n implies C_m). The hard direction, showing that C_n does not imply C_m, is really hard--- it involves constructing models of set theory where C_n is true but C_m is not. These proofs are wisely omitted.

Chapter 43 is titled DENIS THERIEN: SOLVABLE GROUPS. Recall that the complex numbers are algebraically closed. Let us put that a different way: If you want to solve a polynomial p(x)=0 over the rationals then there will be a large enough field extension of the rationals where it has a root.

What if you are trying to solve a group equation over a group, such as ax=bx over S_5 x S_7 where a=(1 2 3 4) and b=(1 3)(1 5). (I honestly do not know if that has a solution). If there is no solution then is there some group that contains S_5 x  S_7 as a subgroup where there is a solution? For this equation I do not know. But more to the point, is there some general theorem that says you can always find a larger group with a solution? NO. In this chapter they give an example where you cannot find a larger group (and they prove it works--- it's not that hard) and state some theorems and conjectures about this issue.

Both Chapter 37 and Chapter 43 were excellent since they told me about a problem I had not thought of but once introduced were very interesting. In both cases they gave me a simple proof that I could follow. I plan to read more on these topics. Tomorrow.

TIM ANDRER GRAN: Is the math serious or recreational?

BILL G: To understand the statements of the theorems you need to know some math, say that of a sophomore math major. Even then, some terms would have to be explained to you. So you might say the statements (not the proofs) are recreational to people who read Martin Gardner's or Ian Stewart's columns AND went on to learn some more math.

ANA WRITSET: Why are the names of the comments so odd? Even mine!

BILL G: Aside from Bill G'' Not Porn'', and Colbert Nation'' all of the names are anagrams. Some of the anagrams are from the April 1, 2014 post on the Godel's Lost Letter Blog (Lipton-Regan blog)  and some are from an April 1, 2013 post (more properly, a paper pointed to from that post) of computationalcomplexity blog (Fortnow-Gasarch blog).

FIFTH  POST: WHO SHOULD BUY THIS BOOK?}

If you are an undergraduate in math or CS (and like theory) then this book will tell you some tips on how to get started in research and give you some nice topics to read up on, though some may be hard. As you go from ugrad to grad student to professional the light chapters will get less interesting and the heavy chapters will get more interesting. I think Lipton and Regan have calculated the exact right balance so the book is good for anyone.

## Thursday, May 22, 2014

### Theory Jobs 2014

In the fall we list theory jobs, in the spring we see who got them. Similar to last year, I created a fully editable Google Spreadsheet to crowd source who is going where. Same rules as last year:
• I set up separate sheets for faculty, industry, postdoc/visitors and students.
• People should be connected to theoretical computer science, broadly defined.
• Only add jobs that you are absolutely sure have been offered and accepted. This is not the place for speculation and rumors.
• You are welcome to add yourself, or people your department has hired.
This document will continue to grow as more jobs settle. So check it often.

Edit

## Sunday, May 18, 2014

### ''4col \le 3col is counter-intuitive and makes me sad'' NOT ANYMORE!

(ADDED LATER- THE PROOF BELOW SEEMS TO BE WRONG- A COMMENTER POINTED OUT A MISTAKE. IF YOU CAN FIX IT PLEASE
LEAVE COMMENT. I WILL POINT OUT MISTAKE WHEN IT COMES.)

FINAL ADD: I DID THE PROOF IN LATEX HERE

A COMMENTER POINTED OUT THAT LOVASZ HAD A SANE PROOF A LONG TIME AGO.
IT GOES THROUGH HYPERGRAPHS. Here is a link to his paper.

In my ugrad theory class (reg,P,NP,Dec,c.e) I proved that SAT is NP-complete. In the next lecture I proved that  SAT \le 3-col, so 3-col is NP-complete. I then proved 3-col \le 4-col. I was planning on proving 4-col \le 3-col but a student beat me to it (I love when that happens!).A student asked

Is 4-col \le 3-col ?

So I did the obvious thing--- we discussed it and we VOTED on it. After the vote I asked one of the naysayers to say why NO. He said that he really couldn't see how you could do anything  reasonable to get 4-col\le 3-col. I told him he was RIGHT but he was WRONG. Say what?

I told him that 4-col \le 3-col but the reduction is INSANE as it goes 4-col \le SAT (since SAT is NP-complete) and then SAT \le 3-col, as I just showed.   So the student is RIGHT in that there is no easy way to do it' (that statement is informal) but was WRONG since YES 4-col \le 3-col. He WAS onto something and I wanted to make sure he knew that, even though he was wrong.

He understood all of this, but later when I had students tell me their FAV and LEAST FAV things in the course he wrote Least FAV: 4-col \le 3-col: it's counter intuitive and makes me sad.(Side note: The women who sits next to him in class wrote that 4-col \le 3-col is her FAV part of the course.)

I have asked myself and some people if there is a SANE reduction 4-col \le 3-col. I must not have asked that many people or thought about it myself that hard, since now that I was inspired to make this student happy I came up with an UTTERLY SANE reduction:

Given G on vertices v(1),....,v(n) and edge set E we construct G' : G is 4-col iff G' is 3-col.

Vertices of G': For all 1\le i \le n vertices v(i,1), v(i,2), v(i,3), v(i,4). Also  vertices  T, F, and R. The colors will be T, F,R. We think of coloring v(i,3) T as meaning that in G node i is colored 3. (I will add more vertices later)

Edges of G' : The vertices T, F, R are all connected, so they are a triangle. Every v(i,j) nodes is connected by an edge to R. To make sure that every vertex of G gets at most one color we have for all 1\le i\le n the edges

UPDATE- THE REST OF THIS POST IS STUFF I ADDED LATER WHICH I BELIEVE IS NOW A CORRECT PROOF.

KEY- there is a gadget GADF(x,y) such that if x and y are both F then it
has an output node that is F. AND there is a gadget GADT(x,y) such that if both x,y are T then it has an output node that is T. GADF is used in the usual proof that SAT \le 3-COL.  GADT I have never seen used but it is a trivial variant of GADF.

To make sure that at least one of v11, v12, v13, v14 is T, use GADF the same way as in the usual ST \le 3-COL proof: GADF(GADF(v11,v12),GADF(v13,v14))
and have the output be connected to both F and R.

To make sure that at most one of v11, v12, v13, v14 is T have

GADT(v11,v12) connect output to both T and R

GADT(v11,v13) connect output to both T and R

How to deal with the edges of G ? My original proof was wrong here as well.
But easily fixed with the gadgets. For all edges (vi,vj) in G we need to make
sure that vi1 and vj1 are NOT both T, vi2 and vj2 are NOT both T, vi3 and vj3 are NOT both T, vi4 and vj4 are NOT both T. use GADT and connect to T,R
for all four of these.

THANKS to all who pointed out mistakes in the original and I HOPE that the current one is correct.

I LEAVE the mess I had before so that comments on it below still make sense,
though if you are reading this for the first time can skip.
(v(i,1),v(i,2)),
(v(i,1),v(i,3)),
(v(i,1),v(i,4)).
(v(i,2),v(i,3)),
(v(i,2),v(i,4)),
(v(i,3),v(i,4)),

THIS IS THE PROBLEM- I WANTED TO MAKE SURE THAT ONLY ONE OF
v(i,1), v(i,2), v(i,3), v(i,4) WAS TRUE. BUT THE WAY THAT I DO IT I
CREATE A 5-CLIQUE WITH THESE VERTICES AND R.
SO NEED A WAY TO MAKE SURE THAT ONLY ONE OF THESE IS TRUE
WHILE MAKING SURE GRAPH IS STILL 3-COL. GADGET SIMILAR TO THE
ONE TO MAKE SURE THAT AT LEAST ONE IS T (USED IN SAT\le 3-COL
AND LATER IN THIS PROOF) MIGHT WORK.

To make sure that at least one of v(i,1), v(i,2), v(i,3), v(i,4) use the same gadget used in the proof that SAT \le 3-col. (This will introduce some more vertices and edges.)
THATS THE ENTIRE CONSTRUCTION!

Now he is happy and I am happy that he is happy!

Note that this generalizes to c-col \le 3-col.

## Thursday, May 15, 2014

### Losing the Middle

In the 70's growing up, to listen to music I had a turntable for vinyl records. The quality of music went up almost continuously with the amount you were willing to spend. In the mid-80's we had digital compact discs and we saw a big change. You could get pretty good quality music at a relatively low cost. If you wanted great quality you would still use vinyl and high-priced needles and audio systems. The middle disappeared, either you were fine with the CD quality or you went for a high end sound.

You see the same with photography. Back in the 70's I had a small darkroom and a mid-level camera. Again the more you spent the better quality you got. Now most people are satisfied with their Smartphones for taking pictures, or you spend significant more money for a high-end camera. There is a continuous improvement from high-end to very high end but it makes little sense to buy a \$300 camera these days.

For video games, you either use your games on your phone or tablet, or splurge on a system like Xbox or Playstation. Same for watching television shows and movies. You even see this phenomenon in cars where even the low-end models have a solid baseline of digital systems and safety. There are still some things you can't digitize, like wine, where you still have a continuous improvement spectrum.

So what's the problem, after all everyone now gets better quality at lower cost, whatever the price point. Let's go back to the music example. You'd start off with a cheap system and then as you earned some money you'd splurge on a better needle and get an improvement in quality. And you'd keep improving until you reached a high-level sound.

Now many people would never take that step from an iPhone to vinyl because it requires a large investment to get any improvement in sound. They'll never find out what they're missing.

## Monday, May 12, 2014

### How should qualifying exams and courses work

In my last post about what Every Theory Grad Student Should know some more general questions were raised:

Qualifying exams vs Course Requirements.
Why do we have either?

1)  To correct mistakes that admissions made. That is, some students that were admitted are not going to finish and better to get them out of the system sooner rather than later.

2) To make sure students are well rounded.

When do exams work:
In Math or Physics there is a well defined notion of basic stuff that all grad students should know. That's why, for the most part, every Math prof can teach every ugrad math course. That a Logician Teaches Linear Algebra does not surprise anyone.

CON for CS exam:
In CS... we have not settled on an every CS grad student must know...' I suspect we haven't because the field changes fast AND  our field is just so diverse. Hence  NOT  every CS prof could PASS every ugrad CS course. In short- having a qualifying exam may be problematic since we don't quite know what  the basics are

CON for  exams:
You are getting rid of people. Are they the right people?

Would you believe that someone we  kicked out of the program had four papers in STOC! Would you believe it! Four papers in STOC! No. Oh. Would you believe 2 papers in ICALP? No. How about a failed proof that P=NP?

Where do you draw the line for she's so good we should let her get a PhD even though they failed the qualifying exams' This doesn't happen in math so much since they don't start research their first year. Again, the difference is the age of the field and the prereq needed to get up to speed.

PRO for exams:
You get rid of people early before they waste too much time.

PRO for courses: If you take Blah courses in blah blah areas then even if you try to game the system some, you do KNOW something.

CAVEAT about courses: If the course grades actually matter for the requirements then the professor has to give out real HW and real exams. This forces people to learn the material-- even grad students need some encouragement. But  it may be bad for the learning environment.

## Thursday, May 08, 2014

### 1984 + 30

Back in 7th grade we had some discussion in history class long since forgotten but was ended by the statement "Remember, 1984 is only eight years away". While the rumor had it George Orwell picked the title 1984 from switching the last two digits from the year he wrote the book, 1984 the year loomed large ahead in that cold war world we lived in.

1984 the year itself came and went without much hoopla beyond a unmemorable movie adaptation.

I was reminded of 1984 by a recent play adapted from the book at Brandeis where my daughter now attends. They told the story quite effectively in flashback during the torture of Winston Smith.

And now we sit three decades later with revelations that the NSA track who we call and contact and Google knows nearly everything about me, including where I am at all times. Dave Eggers recent novel The Circle draws a rather direct line from the Internet giants of today to the world of 1984.

The Internet also offers the greatest deterrent to 1984, encouraging free-flowing quick dissemination of information and ideas, at least in the countries that allow it.

We've hit the technical capabilities both to enable and prevent 1984. So what happens next?

## Wednesday, May 07, 2014

### Every Theory Grad Student should know...

This semester my Graduate Complexity Course has nine students in it.
It had not been offered for two years (when it had around 20) so the demand,
such as it is, should have built up. Of my 9 students only about 4 are theorists.

Why did the UMCP Grad Students in theory NOT take grad complexity?
(I am regarded as a good teacher so I'm  not the reason.)
The reason is that there were two competing grad theory courses in terms of the requirements - Algorithmic Game Theory and Comp Bio.

This raises the question which I ask, as always, non-rhetorically. Is a theory grad student in ALGORITHMS, who is NOT working in Alg Game Theory better off taking Grad Complexity or Alg Game Theory? Alg Game Theory (or some other
type of algorithms course that is not quite what she does)  is perhaps more in their interest and perhaps more the kind of thing she might switch to later. But
every theory grad student should know complexity theory', or more precisely
every theory grad student in algorithms should know about lower bounds on algorithms, e.g., PCP, aproximatin lower bounds, maybe a few other things like Unique Game Conj and some concrete lower bounds' This is true philosophically but time is short.

My course has in it (1) Complexity classes L, NL, P, NP, PSPACE, EXPSPACE some problems complete there and all known relations, (2) All of the machinery to do GI NPC implies  PH collapses, (3) PCP and lower bounds on approximation.
(DO NOT prove the full PCP theorem). If time permits I may do some concrete lower bounds (PARITY not in constant depth or some Proof Theory lower bounds). OH, I may do SHARP P and Toda's theorem also, but this semester we had some snow days and that ended up not being done, though I did do
Valiant-Vazarani and told them ABOUT SHARP P without proofs.

When Jon Katz teaches it I think he does some Derandomization and no concrete lower bounds (JON- if you are reading this you an comment and correct me).

The question of Comp Theory VS ALG Game Theory is really asking how well rounded one should be and in what sense. Someone who works on Approx Algs who takes Alg Game Theory could say that this DOES make them well rounded. Complexity theory is further away from their interests and from anything they may work on, but every theory grad student should know it' Or should they?

I am not complaining about having only nine students (I don't have a TA so I
do all of the grading- so in that sense its great!) but I ask YOU the question,
how important is Complexity Theory (my course or perhaps some other  course) for a grad student in algorithms to know?

## Sunday, May 04, 2014

### (IEEE) Conference on Computational Complexity

The 29th IEEE Conference on Computational Complexity will be held in Vancouver June 11-13. Student travel award deadline is TOMORROW Monday May 5th extended to May 9, early registration deadline is May 17. Don't buy your airline tickets before you read the rest of this post.

The results of a non-binding electronic vote showed 60% would prefer going independent from any society with most of the rest recommending a joint ACM/IEEE meeting. Going independent is far from free, it requires considerable volunteer hours every year to keep the conference going and only 17% of the respondents indicated a willingness to help. The steering committee is asking for volunteer commitments by May 8 and also potential donations to provide start-up funds for an independent symposium. There may be an organizational meeting preceding or following the conference, watch the home page for details.

## Thursday, May 01, 2014

### Favorite Theorems: Equilibrium

The past decade has seen an explosion of work tying together theoretical computer science and micro-economics. Much has come in the area of market design, where tools and ideas from the algorithms community apply nicely in developing auctions that achieve some close to idea outcome.

In complexity, the most exciting work studied the problem of finding equilibriums of games. How does one find a Nash Equilibrium when each player's payoffs are given by a matrix. In a 2-player zero-sum game (my gain is your loss), one can easily find equilibriums using linear programming. But if we have unrelated payoffs, computing the equilibrium can be much more difficult.
Daskalakis et al. showed that computing the Nash Equilibrium between three players in PPAD-complete and Chen and Deng extended their work to 2-player games. PPAD represents a search problem, solvable if P = NP though not believed to be NP-hard.

You don't have to know the formal definition of PPAD to appreciate this work. PPAD corresponds to a discrete version of the Brouwer fixed-point theorem, the critical tool in proving that Nash Equilibriums exist. One proof of the fixed-point theorem uses Sperner's Lemma, also PPAD-complete. The New York Times has a nice example of using Sperner's Lemma to fairly divide up the rent among three friends who share an apartment with different sized rooms.

Paul Goldberg wrote a nice survey on these and related results, such as finding equilibria in markets.