## maximum of a Dirichlet vector

Posted in Books, Statistics with tags , , , , , , , on September 26, 2016 by xi'an

An intriguing question on Stack Exchange this weekend, about the distribution of max{p¹,p²,…}the maximum component of a Dirichlet vector Dir(a¹,a²,…) with arbitrary hyper-parameters. Writing the density of this random variable is feasible, using its connection with a Gamma vector, but I could not find a closed-form expression. If there is such an expression, it may follow from the many properties of the Dirichlet distribution and I’d be interested in learning about it. (Very nice stamp, by the way! I wonder if the original formula was made with LaTeX…)

## bibTeX and homonymy

Posted in Books, University life with tags , , , , on October 31, 2015 by xi'an

How comes BibTeX is unable to spot homonyms?! Namely, if I quote two of my 1996 papers in the same LaTeX document, they will appear as Robert (1996a) and Robert (1996b). However, if I quote two different authors (or groups of authors) with the same surname, Martin as in the above example, who both happened to write a paper in 2014, BibTeX returns Martin (2014) and Martin (2014) in the output, hence it fails to recognise they are different authors, which is just weird! At least for author-year styles. I looked on Stack Exchange TeX forum, but the solution I found did not work with the IMS and Springer styles.

## capacity exceeded…

Posted in Books, University life with tags , , , on April 23, 2015 by xi'an

A silly LaTeX error took me a few minutes too many to solve: I defined

\renewcommand\theta{\boldsymbol{\theta}}


which got me the error message

TeX capacity exceeded ,
sorry [ grouping levels =255].


that I understood as a recursive definition. So I instead pre-defined the new θ as

\newcommand\btheta{\boldsymbol{\theta}}
\renewcommand\theta\btheta


which did not work either… After google-ing the issue, I found this on-line LaTeX Wikibook that provided me with the solution:

\let\btheta{\boldsymbol{\theta}}
\renewcommand\theta\btheta


which worked. Of course, a global change of \theta into \btheta would have been much much faster to execute….

## some LaTeX tricks

Posted in Books, Kids, Statistics, University life with tags , , , , on November 21, 2014 by xi'an

Here are a few LaTeX tricks I learned or rediscovered when working on several papers the past week:

1. I am always forgetting how to make aligned equations with a single equation number, so I found this solution on the TeX forum of stackexchange, Namely use the equation environment and then an aligned environment inside. Or the split environment. But it does not always work…
2. Another frustrating black hole is how to deal with integral signs that do not adapt to the integrand. Too bad we cannot use \left\int, really! Another stackexchange question led me to the bigints package. Not perfect though.
3. Pierre Pudlo also showed me the commands \graphicspath{{dir1}{dir2}} and \DeclareGraphicsExtensions{.pdf,.png,.jpg} to avoid coding the entire path to each image and to put an order on the extension type, respectively. The second one is fairly handy when working on drafts. The first one does not seem to work with symbolic links, though…

## BibTool on the air

Posted in Books, Linux, Travel, University life with tags , , , , , , , , , , on October 23, 2014 by xi'an

Yesterday night, just before leaving for Coventry, I realised I had about 30 versions of my “mother of all .bib” bib file, spread over directories and with broken links with the original mother file… (I mean, I always create bib files in new directories by a hard link,

    ln ~/mother.bib

but they eventually and inexplicably end up with a life of their own!) So I decided a Spring clean-up was in order and installed BibTool on my Linux machine to gather all those versions into a new encompassing all-inclusive bib reference. I did not take advantage of the many possibilities of the program, written by Gerd Neugebauer, but it certainly solved my problem: once I realised I had to set the variates

check.double = on
check.double.delete = on
pass.comments = off

all I had to do was to call

bibtool -s -i ../*/*.bib -o mother.bib
bibtool -d -i mother.bib -o mother.bib
bibtool -s -i mother.bib -o mother.bib


to merge all bib file and then to get rid of the duplicated entries in mother.bib (the -d option commented out the duplicates and the second call with -s removed them). And to remove the duplicated definitions in the preamble of the file. This took me very little time in the RER train from Paris-Dauphine (where I taught this morning, having a hard time to make the students envision the empirical cdf as an average of Dirac masses!) to Roissy airport, in contrast with my pedestrian replacement of all stray siblings of the mother bib into new proper hard links, one by one. I am sure there is a bash command that could have done it in one line, but I spent instead my flight to Birmingham switching all existing bib files, one by one…

## unicode in LaTeX

Posted in Books, Linux, Statistics, University life with tags , , , , , , on October 9, 2014 by xi'an

As I was hurriedly trying to cram several ‘Og posts into a conference paper (!), I looked around for a way of including Unicode characters straight away. And found this solution on StackExchange:

\usepackage[mathletters]{ucs}
\usepackage[utf8x]{inputenc}

which just suited me fine!

## a weird beamer feature…

Posted in Books, Kids, Linux, R, Statistics, University life with tags , , , , , , , , , , , , on September 24, 2014 by xi'an

As I was preparing my slides for my third year undergraduate stat course, I got a weird error that got a search on the Web to unravel:

! Extra }, or forgotten \endgroup.
\endframe ->\egroup
\begingroup \def \@currenvir {frame}
l.23 \end{frame}
\begin{slide}
?


which was related with a fragile environment

\begin{frame}[fragile]
\frametitle{simulation in practice}
\begin{itemize}
\item For a given distribution $F$, call the corresponding
pseudo-random generator in an arbitrary computer language
\begin{verbatim}
> x=rnorm(10)
> x
[1] -0.021573 -1.134735  1.359812 -0.887579
[7] -0.749418  0.506298  0.835791  0.472144
\end{verbatim}
\item use the sample as a statistician would
\begin{verbatim}
> mean(x)
[1] 0.004892123
> var(x)
[1] 0.8034657
\end{verbatim}
to approximate quantities related with $F$
\end{itemize}
\end{frame}\begin{frame}


but not directly the verbatim part: the reason for the bug was that the \end{frame} command did not have a line by itself! Which is one rare occurrence where the carriage return has an impact in LaTeX, as far as I know… (The same bug appears when there is an indentation at the beginning of the line. Weird!) [Another annoying feature is wordpress turning > into &gt; in the sourcecode environment…]