Computational Complexity
Computational Complexity and other fun stuff in math and computer science from Lance Fortnow and Bill Gasarch
Thursday, June 06, 2024
The Godzilla Moment
Monday, June 03, 2024
FOCS 2024 Test of Time Award. Call for nominations and my opinion
The call for nominations for the Test of Time Award at FOCS 2024 has been posted here.
Eligibility and past winners are here.
Points
1) It is good to have an award that waits until the dust settles and we can see what was really important.
2) The winners are all excellent papers that really have passed the test of time.
3) And of course it is really important that they appeared in FOCS. NO IT ISN"T! See next point
4) I would prefer a test-of-time award that is independent of WHERE the paper first appeared. Tying it to FOCS or STOCS or FOCS-or-STOC seems bad. I would opt for appearing in ANY journal or conference. Appearing in a journal of low quality is not a problem since this award should be for papers that are judged on their merit and influence, and not on their pedigree.
5) My proposal to allow any journal or conference may be impractical because some organization has to give it out, and if that organization is IEEE or ACM they will restrict to their own publications.
6) STOC also has a test of time award, see here 76) I tried to find out of the SODA conference has a test of time award but mostly got hits about the Baking Soda Test for determining if a pregnant women is going to have a boy or girl. It actually worlds 50% of the time! See here
7) I was not able to find any other test-of-time award for Comp Sci THEORY.
8) I DID find test of time awards for
SIGCSE- Comp Sci Education, here. Must be for a paper published in a conference co-sponsored by SIGCSE or in an ACM journal. So an excellent paper published elsewhere wouldn't count.
SC2- High Performanc Computing, see here. Paper must have been published in the SC conference.
ACM CCS - Security, Audit(?) and Control, see here I think these must appear in the CCS conference.
Wednesday, May 29, 2024
Double Digit Delights
It started with a post from Fermat's Library.
132 is the sum of all the 2-digit numbers made from its digits. It is the smallest such number. pic.twitter.com/hrByAXbr51
— Fermat's Library (@fermatslibrary) May 26, 2024
My immediate reaction was why not list them all? Giving the smallest such number suggests there are an infinite number of them. But the value of a d-digit number grows exponentially in d, while the 2-digit sum grows quadratically so there must only be a finite number.
Let's be a little more formal. Let's restrict ourselves to positive integers with no leading zeros. The 2-digit sum of x is the sum of all 2-digit numbers formed by concatenating the ith digit of x and the jth digit of x for all i,j with i\(\neq\)j. The 2-digit sum of 132 is 13+12+31+32+21+23 = 132. The 2-digit sum of 121 is 12+11+21+21+11+12 = 88. A number x if 2-idempotent if the 2-digit sum of x is x.
Let's look at the possible lengths of 2-idempotent numbers.
For 1-digit numbers the 2-digit sum is zero.
For 2-digit numbers the 2-digit sum is that number plus another positive number so never equal.
For 5-digit numbers, the 2-digit sum is bounded by 20*99 = 1980 < 10000. So there are no 2-idempotent numbers with 5-digits. More than 5 digits can be discarded similarly.
For 4-digit numbers, the two digit sum is at most 12*99 = 1188. So a 2-idempotent number must begin with a one. Which now bounds it by 19*3+91*3+99*6=924. So there are no 2-idempotent numbers of 4 digits.
So every 2-idempotent must have 3 digits. I wrote up a quick Python program and the only three 2-idempotents are 132, 264 and 396. Note that 264 is 2*132 and 396 is 3*132. That makes sense, if you double every digit and don't generate carries, every two-digit part of the sum also doubles.
Biscuit asks if there is some mathematical argument that avoids a computer or manual search. You can cut down the search space. Every length 3 2-idempotent is bounded by 6*99=594 and must be even since every digit appears in the one's position twice. But I don't know how to avoid the search completely.
Two more Python searches: 35964 is the only 3-idempotent number. If you allow leading zeros then 0594 is 2-idempotent. There may (or may not) be infinitely many such numbers.
Sunday, May 26, 2024
National BBQ day vs World Quantum Day
After my post on different holiDAYS, here, such as Talk like a Pirate Day, and Raegan Revor day, two other Days were brought to my attention
1) Lance emailed me about National BBQ day, which is May 16. See here
2) While at a Quantum Computing Prelim I saw a poster for World Quantum Day, which is April 14. See here.
The obvious question: Which of these days is better known? I Googled them again but this time note the number of hits.
I found out that Google seems to have removed that feature!
When using Google on both Firefox and Chrome, I did not get number of hits.
Some points about this
1) Is there a way to turn the number-of-hits feature on?
2) Bing DOES give number of hits.
World Quantum Day: 899,000 hits
National BBQ Day: 418,000 hits
To get a baseline I binged Pi Day. This did not reveal the number of hits. An unscientific set of Bing searches seems to indicate that if the number of hits is large then they are not shown.
Is hits-on-Bing a good measure of popularity? I do not know.
3) Duck Duck Go does not give number of hits. This might be part of their privacy policy.
4) I also noticed a while back that You Tube no longer allows DISLIKES, just likes. That may explain why my Muffin Math song on You Tube (see here), with Lance on the Piano, has 0 dislikes. It does not explain why it got 19 likes.
5) Google said that the number-of-hits is really an approximation and one should not take it too seriously.
YouTube said that (not in these words) the haters caused dislikes to be far more than they should be.
On the one hand, I want to know those numbers. On the other hand I think Google and YouTube are right about about the numbers not being that accurate. And more so for Bing which is used less so (I assume) has less data to work from.
6) Back to my question: What is better known National BBQ day or World Quantum Day? The nation and the world may never know.
7) All of the above is speculation.
Wednesday, May 22, 2024
Peer Review
Daniel Lemire wrote a blog post Peer Review is Not the Gold Standard in Science. I wonder who was claiming it was. There is whole section of an online Responsible Conduct in Research we are required to take on peer review which discussing its challenges: "honesty, objectivity, quality control, confidentiality and security, fairness, bias, conflicts of interest, editorial independence, and professionalism". With apologies to Winston Churchill, Peer Review is the worst form of measuring academic quality, except for all of the others.
Peer review requires answering two questions.
- Has the research been done properly?
- What is the value of the research?
Sunday, May 19, 2024
I don't do that well when the Jeopardy category is Math
BILL: Not clear.
Wednesday, May 15, 2024
Jim Simons (1938-2024)
While his academic research focused on manifolds, Simons and his foundation had theoretical computer science as one of its priorities and helped fund and promote our field on several fronts.
Foremost of course is the Simons Institute, a center for collaborative research in theoretical computer science. Announced as a competition in 2010 (I was on team Chicago) with the foundation eventually landing on UC Berkeley's campus. At the time, I wrote "this will be a game changer for CS theory" if anything proven to be an understatement over the last dozen years.
Beyond the institute, the Simons Foundation has funded a number of theorists through their investigator and other programs.
Let's not forget Quanta Magazine, an online science publication funded by the foundation without subscriptions or paywalls while science journalism has been seeing cuts elsewhere. Quanta has been particularly friendly to the computational complexity community such as this recent article on Russell and his worlds.
The Simons Foundation will continue strong even without its founder. But as we see challenges in government funding, how much can or should we count on wealthy patrons to support our field?
Read more on Jim Simons from Scott, Dick, the foundation and the institute.
Saturday, May 11, 2024
What is Closed Form? The Horse Numbers are an illustration
In the book Those Fascinating Numbers by Jean-Marie De Konick they find interesting (or `interesting') things to say about many numbers. I reviewed the book in a SIGACT News book review column here. The entry for 13 is odd: 13 is the third Horse Number. The nth Horse number is the number of ways n horses can finish a race. You might think: OH, that's just n!. AH- horses can tie. So it's the number of ways to order n objects allowing ties.
Is there a closed form for H(n)? We will come back to that later.
0) The Wikipedia Entry on horse races that ended in a dead heat is here. They list 78 dead heats (two horses tie for first place) and 10 triple dead heats (three horses tie for first place). For the horse numbers we care if (say) two horses tie for 4th place. In reality nobody cares about that.
1) I have found nowhere else where these numbers are called The Horse Numbers.
2) They are called the Ordered Bell Numbers. The Wikipedia entry here has some applications.
3) They are also called the Fubini Numbers according to the Ordered Bell Number Wikipedia page.
4) I had not thought about the Horse Numbers for a long time when they came up while I was making slides for the proof that (Q,<) is decidable (the slides are here).
5) There is an OEIS page for the Horse Numbers, though they are called the Ordered Bell Numbers and the Fubini Numbers. It is here. That page says H(n) is asymptotically \(\frac{1}{2}n!(\log_2(e))^{n+1}\) which is approx \(\frac{1}{2}n!(1.44)^{n+1}\).
6) There is a recurrence for the Horse Numbers:
H(0)=1
H(1)=1
H(2)=3
For all \(n\ge 3\) we split H(n) into what happens if i horses are tied for last place (choose i out of n) and if the rest are ordered H(n-i) ways. Hence
\( H(n) = \binom{n}{1}H(n-1) + \binom{n}{2}H(n-2) + \cdots + \binom{n}{n}H(0) \)
Using \(\binom{n}{i} = \binom{n}{n-i}\) we get
\( H(n) = \binom{n}{0}H(0) + \binom{n}{1}H(1) + \cdots + \binom{n}{n-1}H(n-1) \)
STUDENT: Is there a closed form for H(n)?
BILL: Yes. Its H(n).
STUDENT: That's not closed form.
BILL: Is there a closed form for the number of ways to choose i items out of n?
STUDENT: Yes, \(\binom{n}{i}\) or \( \frac{n!}{i!(n-i)!}\)
BILL: Does that let you compute it easily? No. The way you compute \(\binom{n}{i}\) is with a recurrence. The way you compute H(n) is with a recurrence. Just having a nice notation for something does not mean you have a closed form for it.
STUDENT: I disagree! We know what n! is!
BILL: Do not be seduced by the familiarity of the notation.