ABC in Svalbard [#2]
The second day of the ABC wwworkshop got a better start than yesterday [for me] as I managed to bike to Dauphine early enough to watch the end of Gael’s...continue reading.
Author: xi'an
ABC in Svalbard [#1]
It started a bit awkwardly for me as I ran late, having accidentally switched to UK time the previous evening (despite a record-breaking biking-time to the University!), then the welcome...continue reading.
plusquamperfect squares
A perfect riddle: For some perfect squares, when you remove the last digit, you get another perfect square. The first five perfect squares are 16, 49, 169, 256 and 361....continue reading.
composition versus inversion
While trying to convey to an OP on X validated why the inversion method was not always the panacea in pseudo-random generation, I took the example of a mixture of...continue reading.
handbook of mixture analysis [review]
“In my opinion, the editors have done an excellent job when selecting the contents of the handbook and putting the different chapters together. For instance, this can be appreciated by...continue reading.
more, please!
As The Riddler proposed for several weeks a CrossProduct™ puzzle when 3 x n one-digit integers have to be deduced from their rowwise and columnwise products, I attempted at writing...continue reading.
folded Normals
While having breakfast (after an early morn swim at the vintage La Butte aux Cailles pool, which let me in free!), I noticed a letter to the Editor in the...continue reading.
why does rbinom(1,1) differ from sample(0:1,1) with the same seed?
This rather legitimate question was posted on X validated last week, the answer being that the C codes behind both functions do not use pseudo-random generators in the same manner....continue reading.
easy and uneasy riddles
On 15 January, The Riddler had both a straightforward and a challenging riddles. The first one was to optimise the choice of a real number d with the utility function...continue reading.
wrong algebra for slice sampler
Once more, and thrice alas!, I became aware of a typo in our “Use R!” book through a question on X validated from a reader unable to reproduce the slice...continue reading.
Kempner Fi
A short code-golf challenge led me to learn about the Kempner series, which is the series made of the inverted integers, excluding all those containing the digit 9. Most surprisingly...continue reading.
how many Friday 13th?
A short Riddler’s riddle on the maximum number of Fridays 13th over a calendar year, of which I found 9 by a dumb exploration : bi=c(1:31,1:29,1:31,1:30,1:31,1:30,1:31,1:31,1:30,1:31,1:30,1:31) oy=bi[-60] for(j in 0:(length(cy<-c(bi,oy,oy,oy)…continue reading.
around the table
The Riddler has a variant on the classical (discrete) random walk around a circle where every state (but the starting point) has the same probability 1/(n-1) to be visited last....continue reading.
Bernoulli factory in the Riddler
“Mathematician John von Neumann is credited with figuring out how to take a p biased coin and “simulate” a fair coin. Simply flip the coin twice. If it comes up...continue reading.
the riddle(r) of the certain winner losing in the end
Considering a binary random walk, starting at zero, what is the probability of being almost sure of winning at some point only to lose at the end? This is the...continue reading.
Le Monde puzzle [#1164]
The weekly puzzle from Le Monde is quite similar to older Diophantine episodes (I find myself impossible to point out): Give the maximum integer that cannot be written as 105x+30y+14z....continue reading.
on arithmetic derivations of square roots
An intriguing question made a short-lived appearance on the CodeGolf section of Stack Exchange, before being removed, namely the (most concise possible) coding of an arithmetic derivation of the square...continue reading.
Le Monde puzzle [#1158]
A weekly puzzle from Le Monde on umbrella sharing: Four friends, Antsa, Cyprien, Domoina and Fy, are leaving school to return to their common housing. It is raining and they...continue reading.
asymmetric information
The Riddler of 16 October had the following puzzle: Take a real number θ uniformly distributed over (0,100). Among three players, the winner is whoever guessed the closest price without...continue reading.
sampling w/o replacement except when replacing
Another Riddle(r), considering a box with M myrtle balls and D dandelion balls. Drawing balls without replacement while they stay of the same color as the initial draw, else put...continue reading.
