India’s language battle

Posted in Books, Kids, pictures, Travel with tags , , , , , , , , , , , , , , , , , , , , , , , , , , , , , on January 13, 2023 by xi'an

on [not] making tea

Posted in Travel with tags , , , , , , , , , , , , on November 14, 2021 by xi'an

By chance, when looking for information on the film that usually appears on top of tea brews (!), I came upon this highly ranked blog entry of a security expert explaining how not to make tea. Which did not seem completely right in my tea-oholic eyes..! Not that the following rambling is of any relevance whatsoever!

On the agreement side, it is indeed hard to get decent tea in most places, the primary reason being a lack of understanding that very hot water is needed. The worst being these cafés where they bring you a cup of (definitely not hot) water with a tea bag on the side! I used to travel with my own kettle to avoid this issue, but I am striving to carry as little stuff as possible and hence gave up on that habit. Instead, I often take a thermos bottle that contains an infuser: all that is needed is hot water!

On the disagreement side, the obvious resolution of most complaints about poor quality tea, “herbal teas” that are not tea, tea bags in general, &tc., is to carry your own loose tea. It is light and keeps well and cannot disappoint. And can be brewed several times, especially oolongs. The section about milk is beyond discussion as tea with milk is another beverage altogether. I certainly enjoy drinking duh-wali-chai  in India and am even making some at home from time to time, but otherwise I stopped putting milk in my tea during the first COVID lockdown. (Which also considerably simplified my tea consumption when travelling: all that is needed is hot water!) The main issue is however in using boiling water. Which is almost never recommended for brewing tea! Especially green and Darjeeling teas. Instead of using water above 90⁰, one should stay below 90⁰… Especially when running several brews. Not only this keeps the bitterness under control but it avoids loosing oxygen and CO² contained in the water.

As an aside, this film/sheen is the result of “an interfacial reaction of polyphenols and other components in the tea that bond with ions in the water”.

enjoy a cuppa for International Tea Day

Posted in Mountains, pictures, Travel, Wines with tags , , , , , , , , , , on May 21, 2020 by xi'an

Castleton second flush 2018

Posted in Mountains, pictures, Travel with tags , , , , , , , on October 18, 2018 by xi'an

After receiving an email from the tea dealers Nathmulls in the town of Darjeeling for an offer of the latest summer harvest of F.T.G.F.O.P. Castleton tea, I made a join order of two kilos for my te-addicted colleagues in the maths department in Dauphine, delivery that I found in my office this morning. Truly terrific tea, at about a fifth of the price asked by the major tea chain in Paris!

optimal Bernoulli factory

Posted in Statistics with tags , , , , , , , , , , on January 17, 2017 by xi'an

One of the last arXivals of the year was this paper by Luis Mendo on an optimal algorithm for Bernoulli factory (or Lovàsz‘s or yet Basu‘s) problems, i.e., for producing an unbiased estimate of f(p), 0<p<1, from an unrestricted number of Bernoulli trials with probability p of heads. (See, e.g., Mark Huber’s recent book for background.) This paper drove me to read an older 1999 unpublished document by Wästlund, unpublished because of the overlap with Keane and O’Brien (1994). One interesting gem in this document is that Wästlund produces a Bernoulli factory for the function f(p)=√p, which is not of considerable interest per se, but which was proposed to me as a puzzle by Professor Sinha during my visit to the Department of Statistics at the University of Calcutta. Based on his 1979 paper with P.K. Banerjee. The algorithm is based on a stopping rule N: throw a fair coin until the number of heads n+1 is greater than the number of tails n. The event N=2n+1 occurs with probability

${2n \choose n} \big/ 2^{2n+1}$

[Using a biased coin with probability p to simulate a fair coin is straightforward.] Then flip the original coin n+1 times and produce a result of 1 if at least one toss gives heads. This happens with probability √p.

Mendo generalises Wästlund‘s algorithm to functions expressed as a power series in (1-p)

$f(p)=1-\sum_{i=1}^\infty c_i(1-p)^i$

with the sum of the weights being equal to one. This means proceeding through Bernoulli B(p) generations until one realisation is one or a probability

$c_i\big/1-\sum_{j=1}^{i-1}c_j$

event occurs [which can be derived from a Bernoulli B(p) sequence]. Furthermore, this version achieves asymptotic optimality in the number of tosses, thanks to a form of Cramer-Rao lower bound. (Which makes yet another connection with Kolkata!)