Archive for train

en gare de Tours [jatp]

Posted in pictures, Travel with tags , , , , , , , , , , on August 9, 2020 by xi'an

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chance meeting

Posted in Statistics with tags , , , , , , , , , on July 10, 2018 by xi'an

As I was travelling to Coventry yesterday, I spotted this fellow passenger on the train from Birmingham with a Valencia 9 bag, and a chat with him. It was a pure chance encounter as he was not attending our summer school, but continued down the line. (These bags are quite sturdy and I kept mine until a zipper broke.)

Байкало-Амурская магистраль/БАМ

Posted in Statistics with tags , , , , , , , , , on April 15, 2018 by xi'an

While in Chamonix last month I dropped by the Guérin editions bookstore, always full of tantalising books on climbing and mountaineering, travelling and travellers. I managed to escape with only two small books, one on a young climber stuck for 100 hours at the top of Aiguilles Vertes [not far from my last ice-climb!] and the other one a railway trip along the Baïkal-Amour Mainline (BAM), which goes from the Baïkal Lake to Sovietskaïa Gavan, north of the Trans-Siberian line. The book is not the ultimate travel book as most of the pages are about historical features surrounding this line, first and foremost the constant reminder that Gulag prisoners were relentlessly exploited to build this line, which follows a macabre route along Siberian camps. The trip finishes not at the end of the BAM line or in Vladivostok, but on Sakhaline Island, which was a penitential colony from the mid-1800’s, as covered by Anton Tchekov in a statistical study and a short story, The Murder… (Comments about characters crossed throughout the trip are rarely to the benefit of these characters.) While I do not make this travel book or the places it crosses sound particularly exciting, it still carries with it the inducing whiff of faraway places, which makes me wish I could see Lake Baïkal or Vladivostok one day in the future, if not travel the entire line. And it also brought back memories of Corto Maltese in Siberia, which remains one of my favourites…

self-portrait on a railway board [jatp]

Posted in Kids, Mountains, pictures, Travel with tags , , , , , , on December 31, 2017 by xi'an

an elegant result on exponential spacings

Posted in Statistics with tags , , , , , , , , , , , , , on April 19, 2017 by xi'an

A question on X validated I spotted in the train back from Lyon got me desperately seeking a reference in Devroye’s Generation Bible despite the abyssal wireless and a group of screeching urchins a few seats away from me… The question is about why

\sum_{i=1}^{n}(Y_i - Y_{(1)}) \sim \text{Gamma}(n-1, 1)

when the Y’s are standard exponentials. Since this reminded me immediately of exponential spacings, thanks to our Devroye fan-club reading group in Warwick,  I tried to download Devroye’s Chapter V and managed after a few aborts (and a significant increase in decibels from the family corner). The result by Sukhatme (1937) is in plain sight as Theorem 2.3 and is quite elegant as it relies on the fact that

\sum_{i=1}^n y_i=\sum_{j=1}^n (n-j+1)(y_{(j)}-y_{(j-1)})=\sum_{j=2}^n (y_{(j)}-y_{(1)})

hence sums up as a mere linear change of variables! (Pandurang Vasudeo Sukhatme (1911–1997) was an Indian statistician who worked on human nutrition and got the Guy Medal of the RSS in 1963.)