Archive for rnorm()

a perfectly normally distributed sample

Posted in R, Statistics with tags , , , , , , , , on May 9, 2019 by xi'an

When I saw this title on R-bloggers, I was wondering how “more perfect” a Normal sample could be when compared with the outcome of rnorm(n). Hence went checking the original blog on bayestestR in search of more information. Which was stating nothing more than how to generate a sample is perfectly normal by using the rnorm_perfect function. Still unsure of the meaning, I contacted one of the contributors who replied very quickly

…that’s actually a good question. I would say an empirical sample having characteristics as close as possible to a cannonic gaussian distribution.
and again leaving me hungering for more details. I thus downloaded the package bayestestR and opened the rnorm_perfect function. Which is simply the sequence of n-quantiles
stats::qnorm(seq(1/n, 1 – 1/n, length.out = n), mean, sd)
which I would definitely not call a sample as it has nothing random. And perfect?! Not really, unless one associates randomness and imperfection.

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 > in the sourcecode environment…]