Publications by xi'an
Le Monde puzzle [#1001]
After a long lag (due to my missing the free copies distributed at Paris-Dauphine!), here is a Sudoku-like Le Monde mathematical puzzle: A grid of size (n,n) holds integer values such that any entry larger than 1 is the sum of one term in the same column and one term in the same row. What is the maximal possible value observed in such a grid whe...
1871 sym R (1401 sym/6 pcs) 6 img
Le Monde puzzle [#1000…1025]
Le Monde mathematical puzzle launched a competition to celebrate its 1000th puzzle! A fairly long-term competition as it runs over the 25 coming puzzles (and hence weeks). Starting with puzzle #1001. Here is the 1000th puzzle, not part of the competition: Alice & Bob spend five (identical) vouchers in five different shops, each time buying the m...
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Le Monde puzzle [#1002]
For once and only because it is part of this competition, a geometric Le Monde mathematical puzzle: Given both diagonals of lengths p=105 and q=116, what is the parallelogram with the largest area? and when the perimeter is furthermore constrained to be L=290? This made me jump right away to the quadrilateral page on Wikipedia, which reminds us...
1558 sym R (483 sym/1 pcs) 8 img
Statlearn17, Lyon
Today and tomorrow, I am attending the Statlearn17 conference in Lyon, France. Which is a workshop with one-hour talks on statistics and machine learning. And which makes for the second workshop on machine learning in two weeks! Yesterday there were two tutorials in R, but I only took the train to Lyon this morning: it will be a pleasant opportun...
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optimultiplication [a riddle]
The riddle of this week is about an optimisation of positioning the four digits of a multiplication of two numbers with two digits each and is open to a coding resolution: Four digits are drawn without replacement from {0,1,…,9}, one at a time. What is the optimal strategy to position those four digits, two digits per row, as they are drawn, t...
1979 sym R (928 sym/2 pcs) 4 img
Le Monde puzzle [#1003]
A purely arithmetic Le Monde mathematical puzzle: Find the four integers w, x, y, z such that the four smallest pairwise sums among the six pairwise sums are 59, 65, 66, and 69. Similarly, find the four smallest of the five integers v, x, y, z such that the five smallest pairwise sums among the ten pairwise sums are 56, 64 , 66, 69 and 70. The ...
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a secretary problem with maximum ability
The Riddler of today has a secretary problem, where one measures sequentially N random variables until one deems the current variable to be the largest of the whole sample. The classical secretary problem has a counter-intuitive solution where one first measures N/e random variables without taking any decision and then and only then picks the fir...
1553 sym R (455 sym/1 pcs) 4 img
Le Monde puzzle [#1006]
Once the pseudo-story [noise] removed, a linear programming Le Monde mathematical puzzle: For the integer linear programming problem max 2x¹+2x²+x³+…+x¹⁰ under the constraints x¹>x²+x³, x²>x³+x⁴, …, x⁹>x¹⁰+x¹, x¹⁰>x¹+x² find a solution with the maximal number of positive entries. Expressed this way, it becomes quite...
2252 sym R (260 sym/2 pcs) 6 img
continental divide
While the Riddler puzzle this week was anticlimactic, as it meant filling all digits in the above division towards a null remainder, it came as an interesting illustration of how different division is taught in the US versus France: when I saw the picture above, I had to go and check an American primary school on-line introduction to division, ...
1597 sym R (508 sym/1 pcs) 8 img
datazar
A few weeks ago and then some, I [as occasional blogger!] got contacted by datazar.com to write a piece on this data-sharing platform. I then went and checked what this was all about, having the vague impression this was a platform where I could store and tun R codes, besides dropping collective projects, but from what I quickly read, it sounds m...
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