Thursday, April 02, 2020

Let's Hear It for the Cloud

Since March 19th I have worked out of home. I've had virtual meetings, sometimes seven or eight a day, on Zoom, Bluejeans, Google Hangouts, Google Meet, Blackboard Collaborate Ultra and Microsoft Teams. I take notes on my iPad using Penultimate which syncs with Evernote. I store my files in Dropbox and collaborate in Google Drive. I communicate by Google Chat, Gmail, Facebook messenger and a dozen other platforms. I continue to tweet and occasionally post in this blog. 

A billion of my closest friends around the world are also working out of home and using the same and similar tools. Yet outside of some pretty minor issues, all of these services continue to work and work well. Little of this would have been possible fifteen years ago. 

As Amazon scaled up their web operations to handle their growing business in the early 2000's they realized they could sell computing services. AWS, Amazon Web Services, started in 2006. Microsoft Azure, Google and others followed. These sites powered smartphones and their apps that push heavy processing to the cloud, small startups who don't need to run their own servers, and companies like Zoom when they need to scale up quickly and scale down like Expedia when they don't need as much use. Amazon and Microsoft makes most of their profit on cloud services. Amazon can't get me toilet paper but they can make sure Blackboard continues to work when all of our classes move online. 

Just for fun I like to occasionally look over the large collection of Amazon Cloud Products. Transcribe an audio recording and translate to Portuguese, not a problem. 

The cloud can't allow all of us to work from home. We have many who still go to work including front-line health care workers putting their lives on the line. Many have lost their jobs. Then of course there are those sick with the virus, many of whom will never recover. We can't forget about the reason we stay indoors.

But every now and then it's good to look back and see how a technology has changed our world in a very short time. If we had this virus in the 90's we'd still be having to go to work, or simply stop teaching and other activities all together.

And how will our universities and other work spaces look like in the future now that we find we can work reasonably well from home and even better technologies develop? Only time will tell.

Tuesday, March 31, 2020

Length of Descriptions for DFA, NFA, CFG

We will be looking at the size of descriptions

 For DFAs and NFAs this is the number of states.

For CFG's we will assume they are in Chomsky Normal Form. So for this post CFG means CFG in Chomsky normal form. The length of a Chomsky Normal Form CFL is the number of rules.

1) It is known there is a family of languages L_n such that

DFA for L_n requires roughly 2^n states.

NFA for L_n can be done with roughly n states.

L_n =  (a,b)^* a (a,b)^n

Also note that there is a CFG for L_n with roughly n rules. (one can show this directly or by some theorem that goes from an NFA of size s to a CFG of size roughly s).

So L_n shows there is an exp blowup between DFAs and NFA's

2) It is known that there is a family of languages L_n such that

DFA for L_n requires roughly 2^n states

NFA for L_n requires roughly 2^n states

CFG for L_n can be done with roughly n rules

L_n = { a^{2^n}  }

So L_n shows there is an exp blowup between NFAs and CFGs.

3) Is there a family of languages L_n such that

NFA for L_n requires 2^{2^n} states

CFG for L_n can be done with roughly n rules.

The answer is not quite- and perhaps open.  There is a set of family of languages L_n such that for infinitely many n he above holds. These languages have to do with Turing Machines. In fact, you can replace

2^{2^n}} with any function f  \le_T  INF (so second level of undecidability).

For this blog this is NOT what we are looking for. (For more on this angle see here

4) OPEN (I think) Is there a family of langs L_n such that for ALL n

NFA for L_n requires 2^{2^n} (or some other fast growing function

CFG for L_n can be done with roughly n states (we'll take n^{O(1)})

5) OPEN (I think) Is there a family of langs L_n such that for ALL n
(or even for just inf many n)

DFA for L_n requires 2^{2^n}} states

NFA for L_n requires 2^n states and can be done in 2^n

CFG for L_n can be done with n rules.

(we'll settle for not quite as drastic, but still want to see DFA, NFA, CFG all
far apart).

Saturday, March 28, 2020

Robin Thomas

Graph Theorist and Georgia Tech Math Professor Robin Thomas passed away Thursday after his long battle with ALS. He was one of the giants of the field and a rare double winner of the Fulkerson Prize, for the six-color case of the Hadwiger Conjecture and the proof of the strong perfect graph theorem.

If you start with a graph G and either delete some vertices or merge vertices connected by an edge, you get a minor of G. The Hadwiger conjecture asks whether every graph that is not (k+1)-colorable graph has a clique of size k as a minor. Neil Robertson, Paul Seymour and Thomas proved the k=6 case in 1993 and still the k>6 cases remain open.

A graph G is perfect if for G and all its induced subgraphs, the maximum clique size is equal to its chromatic number. In 2002 Maria Chudnovsky, Robertson, Seymour and Thomas showed that a graph G is not perfect if and only if either G or the complement of G has an induced odd cycle of length greater than 3.

Robin Thomas was already confined to a wheelchair when I arrived at Georgia Tech in 2012. He was incredibly inspiring as he continued to teach and lead the Algorithms, Combinatorics and Optimization PhD program until quite recently. Our department did the ALS challenge for him. In 2016 he received the Class of 1934 Distinguished Professor Award, the highest honor for a professor at Georgia Tech.  He'll be terribly missed.

Tuesday, March 24, 2020

What to do while ``stuck'' at home/Other thoughts on the virus

Lance had a great post on what to do while you are stuck at home, which is of course relevant to whats happening now. Lance's post is here.

I will add to it, and then have other comments.

1) In our current electronic society we can do a lot from home. Don't think of it as being `stuck at home'

2) Lance points out that you should read a paper, read a textbook, etc. I of course agree and add some advice. Be Goldlocks!

This paper is too hard (e.g., a text on quantum gravity)

This paper is too easy (e.g., a discrete  math textbook for a freshman course)

This paper is just right (e.g., working out the large canonical Ramsey theorem)

3) If you catch up on your TV viewing on your DVR then beware: you will see commercials for Bloomberg.

4) DO NOT binge watch TV.  You will hate yourself in the morning.

5) Simons Inst Theory talks:

TCS+ talks


The Gathering for Gardner records all of their talks and puts the on you-tube
so goto youtube and search for Gathering for Gardners. These are Goldilocks talks since they
are easy but on stuff you prob don't know.

6) Keep fit. I used to go on treadmill for 45 minutes a day, now I am doing an hour.

7) Go for walks with a person who already shares your house, but avoid other people.

8) Book reviews, surveys, orig articles, that you were putting off writing- now write them.
but see next item.

10) Catch up on your blog reading. My favorite was Scott Aaronson's blog post about Davos:here. I also read every single comment. I hated myself in the morning. So that part may have been a mistake.


1) Do you really have more free time? No commuting, no teaching, but you still have the rest of your job, and perhaps it is harder if some things are easier at work. And calling relatives and friends to make sure they are okay, and just to talk, is a great thing to do, but its time consuming.

2) I'm beginning to lose track of what day-of-the-week it is since I don't have school to keep me on track, and I only watch TV shows on DVR so I watching a show on a day does not mean I know what day it is.

3) Avoid being price-gouged. The first few days that I tried to buy TP for my mom on amazon (I do this in normal times--- I order lots for my mom on amazon--- she is tech shy. She is also over 90.) her usual brand was out of stock, and the other brands were either higher quality so higher prices or just
absurdly priced. She wisely said to wait a week. She was right- it was easy to get at the usual price.

4) More generally, it seems like the shortages are people-created. For example, if in a store you see they are low on X, then you buy LOTS of X, and everyone does that, so then their really is a shortage of X. But I think thats calmed down some.

5) It important to have a `we will recover from this, life will go on' attitude (while following the things ALL experts say- wash your hands a lot, drink lots of water, get lots of sleep, which is prob
good advice anyway) and hence I will try to, for the next few weeks, blog on NORMAL things----Hilberts's 10th problem, Large Ramsey, etc.

ADDED LATER- there is a very nice contrarian view in the comment by Steve, the first comment. You should read that!

Thursday, March 19, 2020

What to do while stuck at home Part I

First of all both the Turing award and Abel Prize announced yesterday.

As we start moving from the panic phase of the coronavirus to the boring phase, what kinds of things should you do or not do while stuck at home for the next two weeks to eighteen months.

First of all still do your job. Teach your online classes. Try to do some research. Meet with your colleagues/students/advisor virtually (best with Zoom or something similar). Submit to conferences. What else? Use the situation for your advantage.

Attend virtual conferences: Really attend. Pretend that you flew there and devote the entire day to going to virtual talks or chatting with other attendees in virtual hallways. I said it wouldn't happen this way last week so prove me wrong.

Create a Virtual Workshop: Because you can. Invite people to give online talks. Open it up for all to listen. Find ways to discuss together.

Connect: Make a virtual get-together with an old colleague or someone you've always wanted to meet. Researchers around the world will be holed up and happy to get some interactions.

Learn Something New: Read a textbook. Take an online course in CS or something completely different. There are plenty.

Help Others Learn: Start that book you've always wanted to write. Or just write a short survey article giving your view of a slice of the theory world. Create some videos or a podcast to explain stuff.

Pick up a hobby: Something outside computer science just to keep your sanity.

Watch some fun computer-related movies: Her, Sneakers, The Computer wore Tennis Shoes, 2001, The Imitation Game, Hidden Figures, Colossus: The Forbin Project, Ex Machina. Add your own favorites in the comments.

And on the other hand don't

Become an epidemiologist: As a computer scientist you are an expert in networks, graph theory and exponential growth so you can create models that show we are grossly under preparing and/or overreacting to the virus and want to tell the world how you are right and the so-called "experts" are wrong. Please don't.

Prove P ≠ NP: Trying to settle P v NP and failing is instructive. Trying to settle P v NP and thinking you succeeded is delusional.

Freak Out: We will get past this virus and the world will recover.

Bill will follow up with his own ideas in part II next week.

Tuesday, March 17, 2020

Richard Guy passed away at the age of 103

Richard Guy passed away on March 9, 2020 at the age of 103. Before he died he was the worlds oldest living mathematician (see here for a list of centenarians who are famous scientists or mathematicians). He was also the oldest active mathematician-- he had a paper on arxiv (see here) in October of 2019.  (ADDED later since a commenter pointed it out to me--- a paper by Berlekamp and Guy posted in 2020: here)

I met him twice- once at a Gathering for Gardner, and once at an AMS meeting. I told him that Berlekamp-Conway-Guy had a great influence on me. He asked if it was a positive or negative influence. He also seemed to like my talk on The Muffin Problem, though he might have been being polite.

I did a blog about Richard Guy on his 103rd birthday, so I recommend readers to go there
for more about him.  One point I want to re-iterate:

Richard Guy thought of himself of an amateur mathematician. If he means someone who does it for love of the subject then this is clearly true.  If it is a measure of how good he is (the term `amateur' is sometimes used as an insult) then it is clearly false. If it means someone who does not have formal training than it is partially true.

Thursday, March 12, 2020

The Importance of Networking

People skip conferences because of the coronavirus or for global warming or just because conferences are too expensive and time consuming. I'm certainly no fan of the current conference structure but I would never want to virtualize all of them. Even if we could completely recreate the conference experience in virtual reality, people would not hang out in the halls without the commitment of having made the physical trip. I made this point in a tweet with a depressing response.

I don't disagree with anything Mahdi says except for the "crucial importance". Great ideas come from chance encounters and random conversations. Many of my research papers would never have happened if not for a conversation had at a conference or on the plane or train rides that took me there. Harken Gilles Brassard's origin story of quantum cryptography.
One fine afternoon in late October 1979, I was swimming at the beach of a posh hotel in San Juan, Puerto Rico. Imagine my surprise when this complete stranger swims up to me and starts telling me, without apparent provocation on my part, about Wiesner’s quantum banknotes! This was probably the most bizarre, and certainly the most magical, moment in my professional life6. Within hours, we had found ways to mesh Wiesner’s coding scheme with some of the then-new concepts of public-key cryptography.... The ideas that Bennett and I tossed around on the beach that day resulted in the first paper ever published on quantum cryptography, indeed the paper in which the term “Quantum Cryptography” was coined. 
And Footnote 6 read as follows.
At the risk of taking some of the magic away, I must confess that it was not by accident that Bennett and I were swimming at the same beach in Puerto Rico. We were both there for the 20th Annual IEEE Symposium on the Foundations of Computer Science. Bennett approached me because I was scheduled to give a talk on relativized cryptography on the last day of the Symposium and he thought I might be interested in Wiesner’s ideas. By an amazing coincidence, on my way to San Juan, I had read Martin Gardner’s account of Bennett’s report on Chaitin’s Omega, which had just appeared in the November 1979 “Mathematical Games” column of Scientific American—so, I knew the name but I could not recognize Bennett in that swimmer because I did not know what he looked like.
After we see a slate of conferences held virtually due to the virus, networking may indeed become a thing of the past. But we'll never know the research not done because of people who never connected.

Tuesday, March 10, 2020

Theorist Paul R Young passed away

In the early days of theoretical computer science, say 1960-1990 the main tools used were logic.
This made sense since, early on:

a) Some of the basic notions like DTIME(T(n)), P, NP used Turing Machines in their definitions

b) Some of the basic notions like reductions were modeled after similar concepts in
computability theory.

One of the people who did much work in the interface between Logic and TCS was Paul Young.
He passed away in December. Here are some highlights of his work:

1) One of the first books that covered both computability and complexity:

An Introduction to the general theory of Algorithms
by Machtey and Young.

2) In Computability theory all many-one complete sets are computably isomorphic. Berman and
Hartmanis conjectured that the poly-many-one degree of the NP-complete sets was the same. This
would mean that all NP-complete sets were poly-isom (all of the known ones are).

Mahaney and Young in the paper

Reductions Among Polynomial Isomorphism Types

showed that every many-one poly degree either has one degree or has an infinite number of
degrees in a very complicated way.

3) Recall that a Cook Reduction from A to B allows many queries to B, whereas a Karp Reduction
only allows one query and your answer must be the same sense as the query.
Are there  cases where a Cook reduction is faster? Yes, from the paper

Cook reducibility is faster than Karp Reducibility

by Longpre and Young

(The original title was going to be Cook is Faster than Karp, but it was changed since it invoked
images of Cook and Karp in a footrace.  Hmmm. Which one would be faster?)

4) The Boolean Hierarchy is a hierarchy of iterations of NP sets. What if instead of starting with P
one started with RP (Randomized Poly time). What an intriguing notion! To find out read

Generalized Boolean Hierarchies over RP

by  Alberto Bertoni, Danilo Bruschi, Deborah Joseph, Meera Sitharam, Paul Young

5) There are many more, mostly on the theme of the interaction of logic and computer science.

                       I saw him speak on some of these topics and was inspired by how much one could
take notions of computability and translate them into complexity theory.  The field has gone in a
different direction since then (more combinatorial) but we still use many of the basic concepts
like reducibility.  As such we all owe a debit to Paul Young.

Thursday, March 05, 2020

A New College of Computing at Illinois Tech

In 1890, Chicago South Side pastor Frank Gunsaulus gave a sermon where he said that with a million dollars he could build a school where students of all backgrounds could prepare for meaningful roles in a changing industrial society. One of the congregants, Philip Armour, came up to him after the service and told Gunsaulus that "if you give me five years of your time, I will give you the money." Thus was born the Armour Institute of Technology, the forerunner of the Illinois Institute of Technology.

Today Illinois Tech enters a new chapter, announcing a College of Computing, and I am honored to have been asked to serve as its inaugural dean. The college will take on a horizontal mission, to infuse computation and data science thinking throughout the curriculum in every discipline, while understanding the power, limitations and social implications of the technologies they create. We will significantly grow computing to produce the talent needed for a growing Chicago tech community. The college will develop an agile curriculum to continually reevaluate our offerings as computing technology continues to advance, and develop education as a life-long process where our alumni can always count on Illinois Tech to continually reskill to advance their careers.

We will do it all by keeping the core principle of the original "million-dollar sermon," as important as ever, to prepare students of all backgrounds for meaningful roles in a changing technological society.

Monday, March 02, 2020

Logic examples for your Discrete Math class

(I injured my hand about a month ago so I have had a hard time typing. That is why
I have not blogged for a while. I'm better now but still slow. This is a post I prepared
a while back.)

Here are some examples of English and logic for your discrete math class. Or for mine anyway.

1) A computer programmer leaves work and heads for home. Being the good spouse that he is, he calls  his partner and asks if there's anything that needs to be picked up on the way.

Yes, a gallon of milk and, oh, if they have eggs, get a dozen.

Later he arrives home and stumbles into the kitchen burdened with a dozen gallons of milk. His partner  perplexed, asks him ``why in the world did you buy 12 gallons of milk?''

What did he answer?

When I told this to my class one student said that he should answer:

                                                      I love you too Darling

while that is always a good thing to tell Darling, it is not the answer I had in mind.

The  answer is  here.

2) I saw a headline:

                                                  Rise in faux-incest porn alarming

Give two different interpretations of this sentence. (Note- One you might agree with, the other you will likely disagree with.)

My answer is  here

3) Recently someone was describing what I work on to someone else and he said the following wonderfully ambiguous sentence

                           Bill works on puzzles and games. He also work on cake cutting, to be fair.

Give two different interpretations of this sentence.  My answer is here

4) A common saying is

                           All that glitters is not gold

What does this mean literally? What did they really mean to say? My answer is here.

(I had originally thought this was a quote from the Led Zeppelin song Stairway to Heaven;
however, an astute reader left a comment reminding me that, in that song, they actually
say that there is a lady who believes All that Glitters is Gold. The song implies that she is incorrect, so really
NOT(All that Glitters is Gold) which means (exists x)[x glitters but x is not gold] which actually
IS what they meant to say. Yeah!)

5)When the chess player Bobby Fisher died I saw in one article about him the sentence

                                Bobby Fisher was a terrible anti-semite.

This can be interpreted two ways. What are they? Which one did the writer probably mean? My answer is here

6) When Donald Trump broke the Nuclear Treaty with Iran he said

                              Iran is the worse enabler of terrorist in the mideast

This can be interpreted two ways. What are they? Which one did Trump mean? My answer is here.

7) I saw the headline (see here)

There was actually good news in the War on Women in 2019, news we have to build on in 2020.

This can be interepreted in two ways. This one I leave to you, or read the article.

Sunday, February 16, 2020

Pre-(Publish and Perish)

Guest post by Evangelos Georgiadis

Quite a few posts have recently focused on papers,publications and venues; "optimal" venues for papers under different objective functions,e.g. minimizing carbon footprint while maximizing community building, networking as well as information sharing, see Moshe Vardi.

Here we would like to take a closer look at one of the key assumptions -- the paper. In order to generate a paper, one needs to come up with a result, something novel, fresh or interesting to say. The question that has baffled this author is what represents a conducive or perhaps even optimal setting for generating papers. Since papers come in different flavors ranging from "solid technical papers to risky innovative ones" the settings may vary; but ultimately, what would be interesting to investigate (or for that matter crowdsource) is whether there is a common denominator in terms of setting or environment, a necessary but not sufficient condition (so to speak).

Here are some accounts of others which may be helpful as reference points.

Knuth's papers entitled "Semantics of context free grammar" along with "The analysis of algorithms" represent two instances that suggest research institutes might not provide an optimal environment for idea generation.

As Knuth points out in "Selected Papers on Computer Languages" (Chapter 18, p. 431):
Perhaps new ideas emerge most often from hectic, disorganized activity, when a great many sources of stimulation are present at once -- when numerous deadlines need to be met, and when other miscellaneous activities like child-rearing are also mixed into the agenda.
Knuth goes on to say, that it was challenging to do creative work in office and that finding a few hideaways provided some form of solution -- aka sitting under 'that' oak tree near Lake Lagunita. That said, the inspirational setting for getting into the zone for the aforementioned two papers were provided by (Californian) beaches. Hold that observation. Is this not something we have come across somewhere else ? Fields medalist Stephen Smale in "Chaos: Finding a Horseshoe on the Beaches of Rio" suggests that some of his best work happened at his "beach office". Whether beaches do provide for a good setting remains to be shown; perhaps for very innovative ideas, oceanic freedom is necessary. That said, the author recalls (hopefully accurately enough) an account by the young James H Simons, who attended a conference in Japan in the early days. Instead of choosing a spacious accommodation (which he was able to afford), he restricted himself to the typically confined room type -- not only confined by space, but also pressured by time, young Simons was able to generate an interesting result for that conference. (This probably demonstrates that technical results don't necessarily require 'oceanic freedom'.)

Some meaningful probabilistic advice comes from the fat-tails department, in "The Black Swan" by Nassim Taleb (on page 209) : "Go to parties! If you're a scientist, you will chance upon a remark that might spark a new research. "

Murray Gell-Mann provides an interesting collective account in his Google Tech Talk entitled "On Getting Creative Ideas." He recollects a workshop he attended in 1969 in Aspen that focused on the experience of getting creative ideas, not just among mathematicians and theoretical physicists but also poets and artists. This account seems to neglect the actual setting that might nurture creative thought process, but provides interesting references to people such as Hermann von Helmholtz, who happened to have thought about this topic and partitioned the process in terms of "saturation, incubation and illumination".

For those interested in an account that focuses on the Eureka moments of exclusively mathematicians/theoretical physicists see Jacques Hadamard's book "The Mathematician's Mind". Hadamard iterated on Helmholtz's 3 stage process and it's worth taking a look at what he came up.

At last, what are good venues or workshops for generating papers ? Or let's rephrase that a bit, what type of atmosphere at venues fosters creativity -- what food for thought to provide participants and how to distribute that food for thought over a given day ? Ryan R Williams proposed (as practiced by 34th Bellairs Winter Workshop on Computational Geometry) "... easy problems, informal atmosphere focusing exclusively on thinking about problems in a cycle of down-time where one meets in two intense sessions and have free time otherwise." (This type of setting seems to resonate with the 3 stages of "saturation, incubation and illumination".)

That said, most workshops including the Simons workshops don't seem to follow such a recipe. They are more geared towards the follow-up step, namely, communicating what people have found, rather than collaborating with them to tackle open problems. Perhaps some re-evaluation might be required in how workshops are run.

Thursday, January 23, 2020

The World of Publishing

Bill is out for blogging for a couple of weeks on injured-reserve (he’ll be fine). I put together a quick blog post on what’s happening in the world of publications.

The Trump administration has suggested requiring publishers to make all papers based on US federally-funded publicly available immediately instead of after one year. The Association of American Publishers sent an open letter--how do we maintain the organizations and the people who work there if we give up a major revenue source. The ACM joined the letter which caused quite a backlash forcing the ACM to explain itself, write another letter, and run some webinars about open access the last of which is tomorrow. In the end, this is leading to some good discussions about open access and the financial models of academic societies.

The ACM also has a new policy, three options for what happens when an author changes their name: Maintain separate identities, have the two identities link to each other, or retroactively change the name on all previous papers. I can see good reasons for all three options.

Finally Moshe Vardi writes in his CACM column about the ecological cost of conferences and suggests that conferences allow authors to (video)phone it in. Emmanuel Viola offers his own thoughts. Most Conferences will continue to require authors to show up, with only occasional exceptions as needed, believing these policies will keep their conference healthy.

Personally I believe conferences should exist because researchers want to attend, not because they have to. We still need conferences so our community can get together and I don’t believe we can do that via the Internet no matter how good the VR experience gets. But we can have more videos and less conferences and reduce the costs: time, financial and environmental.

Tuesday, January 14, 2020

Quantum Provers to Infinity and Beyond

The Internets are buzzing about the new paper MIP* = RE by Zhengfeng Ji, Anand Natarajan, Thomas Vidick, John Wright and Henry Yuen. See posts by Scott, Boaz, not to mention a wonderful backstory by Vidick himself and a tweet stream by Yeun. I'm not an expert enough to verify or even try to explain the proof so I'll just give a brief overview of the result.

For those not familiar with the classes, RE (recursively enumerable) is the simplest of all complexity classes, a language is in RE if there is some Turing machine M such that x is in L if and only if M on input x accepts. For x not in L, M on x can reject or run forever. The classic halting problem, the set of descriptions of Turing machines that halt on empty input, is RE-complete. To nitpick the notation, it should have been r.e. and even c.e. (computably enumerable), a more standard notation these days. But given the importance of the result, we can give the authors a pass.

MIP* is the set of things provable to a classically random polynomial-time verifier by two separated provers with an unlimited number of quantumly entangled qubits. Without the quantum entanglement, MIP = NEXP, nondeterministic exponential time, and last year Natarajan and Wright showed that MIP* could do at least exponentially better in their paper, NEEXP in MIP*. NEEXP seems large but still only consists of computable sets. RE gets outside of the computable realm.

I found the first paper more surprising, as it showed that quantum entanglement actually gets more, much more, than classical provers. The second paper does get a much stronger and tight result, and still highly surprising in its own right, as it requires disproving the Connes' embedding conjecture. In the end we may just consider this one result, as the second paper subsumes the first both in theorem and authors.

We didn't award the 2019 theorem of the year to Natarajan and Wright, instead opting for a paper that had more, how should I say this, sensitivity. This new paper is certainly the front runner for the 2020 honors, albeit it is only mid-January.

Monday, January 13, 2020

What would you do if you showed P=NP? I would reread Factor Man by Matt Ginsberg

Lance has often said (and also in this) that if P=NP that would be great for the world: much more efficient ways to build things, science could be done better, etc, and that is much more important than that modern crypto would no longer work. We now have the technology to do private key really well--- like a thumb drive that has a billion bits for 1-time pads.

I agree that the world would be better off in some ways, I wonder how much damage would be done in the transition period from public to private key. Would the world recover enough to reap the benefits of P=NP?

First think of what YOU would do if you showed P=NP (and lets assume your algorithm is either reasonable or could be made reasonable with some time and effort).

The novel Factor Man  is about what someone who has solved P=NP does. I won't tell you how it goes, but they deal with the issue intelligently. So if I solved P=NP then I would first re-read it, and think through if I would do that, or modify what is done, or what.  Its a good start.

I reviewed the book in SIGACT News or you can read my review here

On a slightly diff note, here is the latest argument I've heard for why P=NP:

Planar 2-coloring is in P

Planar 4-coloring is in P


Planar 3-coloring should be in P.

This was said by a very good math/cs ugrad at UMCP. I do not know if he was kidding.

Wednesday, January 08, 2020

Silicon Valley Ethics

Spoiler Alert: This post has details from the final episodes of the HBO television series Silicon Valley

A few times I've gotten emails from people claiming they have shown P = NP and asking whether they should keep their algorithm a secret to protect the cryptography out there. My typical response is that they should use their algorithm to mine a few bitcoins and then get back to me.

The fictional characters of Pied Piper faced this dilemma when they AI they created "developed a general solution to discrete log in polynomial time" with some nice complexity class diagrams in the background.

Pied Piper was about to roll out its new internet, a distributed network that communicated between cell phones based on a compression algorithm developed by Pied Piper's CEO. Rolling out the network would reveal even more advanced compression based on breaking discrete log. "If we cancel it or shut it down, then others will try to copy or reverse engineer everything that we've built ... Our launch has to fail, publicly and spectacularly."

But here comes the P v NP dilemma: "And what about all the other stuff we're gonna do? I mean, give internet to underserved communities, students in the homework gap, refugees, genomic research. Pied Piper can help scientists cure cancer."

I'd take broken encryption over cancer any day. You can still do encryption even if P = NP, one-time pads distributed via USB drives or quantum. And cancer sucks.

They should have mined a few bitcoins.

Sunday, January 05, 2020

The Wikipedia Entry on NP-Intermediary Problems lists one of mine! I'm not bragging about it.

I recently needed to look at what NP problems were possibly intermediary (neither in P nor NP-complete). So I went to Wikipedia and found this.

They had many problems, though some I had never heard of. Those that I had never heard of

should they be on the list?

That is, are they natural? That is hard to define rigorously, but I will take you through my train of thought as I read the first few:

Factoring Integers. Yes, quite possibly intermediary: If  its NPC then PH collapses, and, at least so far, does not seem to be in P.  (the NPC--> PH collapse result: We take

FACT = { (n,x) : n has a nontrivial factor ≤ x }

FACT is clearly in NP:
a complete factorization of n provides evidence that some nontrivial factor is \le x.

FACT is clearly in coNP:
a complete factorization of n provides evidence that no nontrivial factor is \le x

so if FACT is NP-complete then SAT is in coNP.

Factoring is clearly an important and well studied problem. It even has its own Wikipedia entry!

Discrete Log. Similar to Factoring. And it is also an important and well studied problem. It even has its own Wikipedia Entry!

Isomorphism Problems They list Group and Ring isomorphism. They don't list Graph, which is odd. (ADDED LATER- my bad, they do mention Graph Isom in the section on Graph Algorithms) Anyway, if Graph Isom is NPC then PH collapses, and, at least so far, there is no algorithm for Graph Isom in P. (I do not think it is know if Group Isom NPC means PH collapses, or if Ring Isom NPC means PH collapses---if you know of such a proof leave a comment and a pointer to it.)

Graph Isomorphism is a well studied problem and seems important and natural (I don't know if Graph Isomorphism has any real applications they way that factoring and DL do).  It even has its own Wikipedia entry! Group and Ring Isomorphism also seem important and natural. And they have their own Wikipedia entry!

Numbers in Boxes Problem My first reaction-Gee, whats that? For the Factoring, DL, and Isomorphism they did not define the problem-- they gave pointers to the Wikipedia entries on them. For this one there was no Wikipedia entry. There was one reference. I went to it. It was a blog entry of mine! Here it is: here, and to save you time I'll say what it is:

{ (1n,1k) : you can partition 1,...,n into k boxes so that no box has x,y,z with x + y = z }

Is this problem important? Does it exist anywhere outside of my blog entry? Yes--- a special case of it was in Dr. Ecco's Cyperpuzzles by Dennis Shasha (note- Dennis was a classmate of mine in graduate school at Harvard). I think the case was to try to partition {1,...,100} as best you can. Actually I first saw the case of the problem in his book and then generalized it.

The problem is sparse so if it was NP-complete then P = NP, very good evidence that its not NPC. And its been studied for thousands of years, with people looking for poly time algorithms (I think Pythagoras studied it) without success, so its almost surely not in P. OR that last sentence was complete nonsense. Indeed, I don't think anyone has studied the problem computationally, or, for that matter, at all. So the evidence that its not in P is... sparse.

But its worse than that. One could devise MANY sparse problems that are, since spares, likely NOT NPC, and hardly studied, so as-of-now, not in P. Should those count? Only if (a) more people study them so there is an attempt to point to to get it into P, and (b) the problem is natural (which is hard to define).

Note that I can vary the problem: x+2y=z (this relates to lower bounds on VDW numbers)
or any other combination of x,y,z or more that I like.

This raises a question:

When is a problem worthy of being put on lists of problems?

Here are some possibly criteria. One can take ANDS and ORS of them.

1) The problem has a Wikipedia entry. This might fall victim to Goodhearts law: when a measure becomes a target, it ceases to be a measure.  That is, I could make a Wikipedia entry on the Number-in-boxes problem and then say LOOK, its on Wikipedia!

2) More than X people have worked on the problem for some value of X. But here is a reason this might not be a good criteria: look at the problem

{ α : α is a reg expression that allows numbers (so a1000 is fine, makes reg expressions  VERY succint) such that L(α)=Σ* }

This problem looks natural, and was proven by Meyer and Stockmeyer to be EXPSPACE complete.
That is the only paper on this problem, yet the problem really does look natural, and the result is rightly celebrated as a natural problem that is provably not in P.

3) When people in the field look at the problem they say YEAH, thats a good problem.

4) The problem relates to other problems or other fields.

I doubt the Number-in-boxes problem satisfies any of these criteria. The variant with x+2y=z relates to Ramsey Theory. Great.

NOW, back to the list-- I won't go through any more on the list, but I note that for some of them the only reference seems to be a conversation on stack-exchange.  Some of those end up referring to real papers so are more likely natural, but some do not.

Having said that, is there any harm in the list having on it some problems that are not ... worthy? Is that even the right word to use?

Note that I don't have strong opinions on any of these matters, I am just wondering what criteria Wikipedia, and other sources, uses, when they have lists of problems.