stéphane carbone [14]

Posted in pictures, Travel, Wines with tags , , , , , , , , on May 28, 2017 by xi'an

Children of Earth and Sky [book review]

Posted in Books, Kids, Travel with tags , , , , , , , , on May 27, 2017 by xi'an

While in Dublin last weekend, I found myself without a book to read and walking by and in a nice bookstore on Grafton Street, I discovered that Guy Gavriel Kay had published a book recently! Now, this was a terrific surprise as his Song for Arbonne was and remains one of my favourite books.

There are similarities in those two books in that they are both inspired by Mediterranean cultures and history, A Song for Arbonne being based upon the Late Medieval courts of Love in Occitany, while Children of Earth and Sky borrows to the century long feud between Venezia and the Ottoman empire, with Croatia stuck in-between. As acknowledged by the author, this novel stemmed from a visit to Croatia and the suggestion to tell the story of local bandits turned into heroes for fighting the Ottomans. Although I found unravelling the numerous borrowings from history and geography a wee bit tiresome, this is a quite enjoyable pseudo-historical novel. Except the plot is too predictable in having all its main characters crossing one another path with clockwise regularity. And all main women character eventually escaping the fate set upon them by highly patriarchal societies.  A Song for Arbonne had more of a tension and urgency, or maybe made me care more for its central characters.

Le Monde puzzle [#1009]

Posted in Books, Kids with tags , , , , on May 26, 2017 by xi'an

An incomprehensible (and again double) Le Monde mathematical puzzle (despite requests to the authors! The details in brackets are mine.):

  1. A [non-circular] chain of 63 papers clips can be broken into sub-chains by freeing one clip [from both neighbours] at a time. At a given stage, considering the set of the lengths of these sub-chains, the collection of all possible sums of these lengths is a subset of {1,…,63}. What is the minimal number of steps to recover the entire set {1,…,63}?  And what is the maximal length L of a chain of paper clips that allows this recovery in 8 steps?
  2.  A tri-colored chain of 200 paper clips starts with a red, a blue and a green clip. Removing one clip every four clips produces a chain of 50 removed clips identical to the chain of 50 first clips of the original chain and a chain of remaining 150 clips identical to the 150 first clips of the original chain. Deduce the number of green, red, and blue clips.

The first question can be easily tackled by random exploration. Pick one number at random between 1 and 63, and keep picking attached clips until the set of sums is {1,…,63}. For instance,

rebreak0]
 sumz=cumsum(sample(difz))
 for (t in 1:1e3)
  sumz=unique(c(sumz,cumsum(sample(difz))))
 if (length(sumz)<63)
    brkz=rebreak(sort(c(brkz,sample((1:63)[-brkz],1))))
 return(brkz)}

where I used sampling to find the set of all possible partial sums. Which leads to a solution with three steps, at positions 5, 22, and 31. This sounds impossibly small but the corresponding lengths are

1 1 1 4 8 16 32

from which one can indeed recover by summation all numbers till 63=2⁶-1. From there, a solution in 8 steps can be found by directly considering the lengths

1 1 1 1 1 1 1 1 9 18=9+8 36=18+17+1 72 144 288 576 1152 2303

whose total sum is 4607. And with breaks

10 29 66 139 284 573 1150 2303

The second puzzle is completely independent. Running another R code reproducing the constraints leads to

tromcol=function(N=200){
  vale=rep(0,N)
  vale[1:3]=1:3
  while (min(vale)==0){
    vale[4*(1:50)]=vale[1:50]
    vale[-(4*(1:50))]=vale[1:150]}
  return(c(sum(vale==1),sum(vale==2),sum(vale==3)))}

and to 120 red clips, 46 blue clips and 34 green clips.

plenary talks at JSM 2017 in Baltimore

Posted in Statistics with tags , , , , , , , , , , on May 25, 2017 by xi'an

ARS: when to update?

Posted in Books, Kids, Statistics, University life with tags , , , , , on May 25, 2017 by xi'an

An email I got today from Heng Zhou wondered about the validity of the above form of the ARS algorithm. As printed in our book Monte Carlo Statistical Methods. The worry is that in the original version of the algorithm the envelope of the log-concave target f(.) is only updated for rejected values. My reply to the question is that there is no difference in the versions towards returning a value simulated from f, since changing the envelope between simulations does not modify the accept-reject nature of the algorithm. There is no issue of dependence between the simulations of this adaptive accept-reject method, all simulations remain independent. The question is rather one about efficiency, namely does it pay to update the envelope(s) when accepting a new value and I think it does because the costly part is the computation of f(x), rather than the call to the piecewise-exponential envelope. Correct me if I am wrong!

Manchester, United we stand!

Posted in Books, Kids with tags , , , , , on May 24, 2017 by xi'an

This is the place
In the north-west of England. It’s ace, it’s the best
And the songs that we sing from the stands, from our bands
Set the whole planet shaking.
Our inventions are legends. There’s nowt we can’t make, and so we make brilliant music
We make brilliant bands

We make goals that make souls leap from seats in the stands
And we make things from steel
And we make things from cotton
And we make people laugh, take the mick summat rotten
And we make you at home
And we make you feel welcome and we make summat happen
And we can’t seem to help it
And if you’re looking from history, then yeah we’ve a wealth

But the Manchester way is to make it yourself.
And make us a record, a new number one
And make us a brew while you’re up, love, go on
And make us feel proud that you’re winning the league
And make us sing louder and make us believe that this is the place that has helped shape the world

And so this is the place now with kids of our own. Some are born here, some drawn here, but they all call it home.
And they’ve covered the cobbles, but they’ll never defeat, all the dreamers and schemers who still teem through these streets.
Because this is a place that has been through some hard times: oppressions, recessions, depressions, and dark times.
But we keep fighting back with Greater Manchester spirit. Northern grit, Northern wit, and Greater Manchester’s lyrics.

Tony Walsh

Russell Maliphant Company

Posted in Kids, pictures with tags , , , , on May 24, 2017 by xi'an

Last weekend, the Russell Maliphant Company from London was performing in a theatre nearby (in our backyard!) and we managed to get tickets at the last minute. While I am not at all versed in modern dance, this was a fantastic experience, with very moving performances from (guest) dancers like Lucia Lacarra and Marlon Dino above, a very elaborate impact of lighting that managed to duplicate or cancel depth, space, and time, great musical tracks, and a unique quality in the movements of the dancers.