Archive for August, 2010

Impressions on Yosemite

Posted in Kids, Mountains, Travel with tags , , , on August 26, 2010 by xi'an

After reading and re-reading Lynn Hill’s Climbing Free: My Life in the Vertical World. and of her ascents in the Yosemite valley, I was definitely looking forward my visit there… While not planning to do any climbing there, I was expecting some out-worldy quality from the place. The first vision of the valley when getting out of the Route 41 tunnel is indeed stunning with the perfect face of El Capitan blocking most of the view. The thousand vertical meters of the face are both daunting and oppressive!

Nonetheless, my overall impression of Yosemite is more one of a gigantic parking lot with nice walls than of a Mecca of big wall climbing… The place is simply bursting at the seams due to the inappropriate number of visitors there and to the complete lack of size control. Cars are parked everywhere, traffic jams block the approaching roads for miles and there are people everywhere one goes… If there is a place where limiting the number of visitors & cars per day would make sense, it is Yosemite. (There are only two access roads and both only lead to the Yosemite valley, so having the Park counting the ins and outs is feasible.) A numerus clausus on the visitors would recover the majesty of the place which has clearly vanished under the cars, garbage bins and flows of shoppers. (By comparison, Banff is also highly popular but the crowd concentrates inside the village, which can be avoided rather easily.) Both hikes I did in the valley were classified as strenuous and very strenuous, respectively, but there were still crowds on both paths, with equipments ranging from the backcountry heavy bagpacks to the flip-flops plus bathing suits. The paths themselves were paved or even tarred, most likely because of the intense traffic they were submitted to. (Even the fairly steep path to the Upper Yosemite Falls that I rounded in a bit more than two hours has its share of unconscious tourists with improper shoes and no water and its paved sections…)

Even the upper range of Glacier Point was victim of the same plague, despite its distance from the centre. Rows of cars, jams at the parking lot at sunset and sunrise, ill-equipped hikers climbing to the top of Sentinel Dome. Except for a deer foraging for food in the valley main parking lot and rodents begging for scraps from hikers, I did not see any sign of wildlife during my week there. Nor did I come across any climber. My most enjoyable moment of the trip was one hour of bouldering in the forest near Yosemite West, where we stayed. By myself.) Terrible impressions, thus, of a Disney-esque caricature of a national park…

Read Paper 13/10/10

Posted in Statistics, University life with tags , , , , on August 25, 2010 by xi'an

There will be an RSS Read Paper session on October 13 given by Marc Girolami and B. Calderhead on Riemann manifold Langevin and Hamiltonian Monte Carlo methods that I definitely plan to attend. Here is the abstract:

The paper proposes Metropolis adjusted Langevin and Hamiltonian Monte Carlo sampling methods defined on the Riemann manifold to resolve the shortcomings of existing Monte Carlo algorithms when sampling from target densities that may be high dimensional and exhibit strong correlations. The methods provide fully automated adaptation mechanisms that circumvent the costly pilot runs that are required to tune proposal densities for Metropolis-Hastings or indeed Hamiltonian Monte Carlo and Metropolis adjusted Langevin algorithms. This allows for highly efficient sampling even in very high dimensions where different scalings may be required for the transient and stationary phases of the Markov chain. The methodology proposed exploits the Riemann geometry of the parameter space of statistical models and thus automatically adapts to the local structure when simulating paths across this manifold, providing highly efficient convergence and exploration of the target density. The performance of these Riemann manifold Monte Carlo methods is rigorously assessed by performing inference on logistic regression models, log-Gaussian Cox point processes, stochastic volatility models and Bayesian estimation of dynamic systems described by non-linear differential equations. Substantial improvements in the time-normalized effective sample size are reported when compared with alternative sampling approaches. MATLAB code that is available from the authors allows replication of all the results reported.

and as usual (400 word) comments can be submitted without any restriction.

Art brut

Posted in Kids, pictures, Travel with tags , , on August 25, 2010 by xi'an

The prodigal mage

Posted in Books, Kids with tags , , , , on August 24, 2010 by xi'an

“Children. How empty our lifes would be without them…and how much less painful.” The prodigal mage

While staying in Yosemite, I read The prodigal mage by Karen Miller. This is a sequel to the Kingmaker Kingbreaker books that I appreciated, even though they were not without flaws. (I prefer the Godspeaker trilogy by the same author, as explained in this post.) This new series of two books has kept the same setting as the initial series, starting with a weak idea that occurs in many sequels, namely that the evil entity the hero(s) must fight is not really dead/destroyed/gone… The (relative) appeal of this new book is that the hero (Asher) is getting old and bad-tempered, as well as more and more reluctant to use his magical powers and that his son Rafel has inherited those powers and does not understand why he could not use them. So, while the overall story is a bit thin, the family plot offers some interest as to the conflict of generations (at least to me as a parent!). Obviously, The prodigal mage is not written by Victor Hugo so the style is not always perfect, with some heavy going dialogues, but this makes for a good vacation read. The second part, The reluctant mage, is already out in hardcover. It (predictably) centers on Rafel’s sister, Deenie, who is also endowed with special powers she’d rather do without, reproducing the pattern observed in her father. However, I will wait for the paperback version and future vacations, looking forward reading soon the third and alas not  last part of Shadowmarch by Tad Williams (which shares a lot with this series, even though the local universe is deeper and more interesting).


Posted in Books, Travel with tags , on August 23, 2010 by xi'an

An interesting tribune in The New York Time of yesterday about locavorism, Math Lessons for Locavores. While I realise the absurdity of buying apples from New Zealand, grean peas from Kenya, or asparagus from Chile when shopping in my local grocery, because equivalent products are or will be available within a few months, I see two flaws with the ultimate locavore theory. The first one is that it is difficult to distinguish from protectionism. My naïve belief is that protectionism, while achieving in the short term a reduction in transportation costs, should have in the long run an adverse ecological impact. In particular because it imposes the production of goods in places where producing those goods are less energy-efficient (using for instance heated greenhouses or artificial irrigation). The second one is that it does not seem to be applying to other goods that are most likely more demanding in energy for their transportation (like cars or clothes) as, if it would, it would be very quickly unsustainable (at least in a democracy). The tribune of Stephen Budiansky is obviously all too optimistic when beaming at the advances of industrial agriculture, since they have been obtained at high ecological costs, as exemplified by the pilfering of Californian aquifers by California growers (I became much more aware of while driving through the parched countryside in the past days!), but he nonetheless has a point, discussed further on his blog.

Ps-Today’s (Sunday, that is!) New York Time contains a paper by Andrew Gelman and co-authors about gay marriage perception.

Death sequence

Posted in Books, Statistics, University life with tags , , , , , , , , , on August 22, 2010 by xi'an

August is not looking kindly at statisticians as I have now learned (after ten days of disconnection) of both Arnold Zellner and John Nelder passing away, on Aug. 11 and 15, respectively. Following this close the death of Julian Besag, this is a sad series of departures of leading figures in the fields of statistics and econometrics. Arnold was 83 and, although I had met him in several Valencia meetings—including one in Alicante where we sat together for breakfast with Persi Diaconis and  where an irate [and well-known ] statistician came to Arnold demanding apologies about comments made late the night before!—, I only had true interactions with him during the past years, over the Jeffreys reassessment I conducted with Judith Rousseau and Nicolas Chopin. On this occasion, Arnold was very kindly helpful, pointing out the volume that he had edited on Jeffreys and that I overlooked, discussing more philosophical points about the early part of Theory of Probability, and making a very nice overview of it at the O’Bayes 09 meeting. Always in the kindest manner. Sid Chib wrote an obituary of Arnold Zellner on the ISBA website (Arnold was the first ISBA president). Andrew Gelman also wrote some personal recollections about Arnold. A memorial site has been set up in his honour.

John Nelder was regularly attending the Read Paper sessions at the RSS and these are the only times I met him. He was an impressive figure in many ways, first and foremost for his monumental Generalised Linear Models with Peter McCullagh, a (difficult and uncompromising) book that I strongly recommend to (i.e. force upon!) my PhD students for its depth. I also remember being quite intimidated the first time I talked with him, failing to understand his arguments so completely that I dreaded later discussions… John Nelder was at  Fisher’s Rothamsted Experimental Station for most of his career and was certainly one of the last genuine Fisherians (despite a fairly rude letter of Fisher to him!).

Tales of the City

Posted in Books, Travel with tags , , , , on August 21, 2010 by xi'an

Tales of the City was on display in a Borders in San Francisco and since I had heard about Armistead Maupin‘s novels in connection with San Francisco, I bought it and read it during our stay in this city. The novel is actually made of a sequence of short dialogues, published as a serial in the San Francisco Chronicle, from 1976 onwards. The dialogues are coherent and sequential in time, revolving around the residents of 28 Barbary Lane. While I liked the immersion of the stories within the city, using a topography I was progressively getting familiar with (incl. the Palace of the Legion of Honor where this picture was taken), I overall disliked the novel very much! The characters are mostly defined through their dialogues with one another and those sound very unreal to me. The part involving the Halcyon magnate and his family sounds like a (poor) 1930 sub-Fitzgerald novel and the forays into the 1970’s gay circles are sounding like a catalogue of SF gay meeting points, at a very superficial level. Another thing that put me off is that the only kid appearing in the whole novel is the victim of a pedophile, while most characters have weird relations with their parents and seem to consider kids a nuisance and only a nuisance… Tales of the City has some comical and witty dialogues and one ends up taking a vague liking to the residents of 28 Barbary Lane, but this does not make enough of a substance for me.