From c8d941c5e988d9b03201fdf864cc6fc616904c62 Mon Sep 17 00:00:00 2001 From: Alexandre Jesus Date: Sat, 2 May 2020 15:15:43 +0100 Subject: [PATCH] Minor fixes --- module2/exo1/toy_document_orgmode_R_en.org | 27 +++++++++++----------- 1 file changed, 13 insertions(+), 14 deletions(-) diff --git a/module2/exo1/toy_document_orgmode_R_en.org b/module2/exo1/toy_document_orgmode_R_en.org index e7f9cbe..d001869 100644 --- a/module2/exo1/toy_document_orgmode_R_en.org +++ b/module2/exo1/toy_document_orgmode_R_en.org @@ -5,37 +5,36 @@ My computer tells me that $\pi$ is approximately -#+BEGIN_SRC R :results output :exports both +#+begin_src R :results output :exports both pi -#+END_SRC +#+end_src #+RESULTS: : [1] 3.141593 * Buffon's needle -Applying the method of Buffon's needle, we get the *approximation* +Applying the method of [[https://en.wikipedia.org/wiki/Buffon%2527s_needle_problem][Buffon's needle]], we get the *approximation* -#+BEGIN_SRC R :results output :exports both +#+begin_src R :results output :exports both set.seed(42) N = 100000 x = runif(N) theta = pi/2*runif(N) 2/(mean(x+sin(theta)>1)) -#+END_SRC +#+end_src #+RESULTS: : [1] 3.14327 * Using a surface fraction argument -A method that is easier to understand and does not make use of the sin -function is based on the fact that if $X \sim U(0,1)$ and $Y \sim -U(0,1)$, then $P[X^2 + Y^2 \le 1] = \pi/4$ (see [[https://en.wikipedia.org/wiki/Monte_Carlo_method]["Monte Carlo method" -on Wikipedia]]). The following code uses this approach +A method that is easier to understand and does not make use of the +$\sin$ function is based on the fact that if $X \sim U(0,1)$ and $Y +\sim U(0,1)$, then $P[X^2 + Y^2 \le 1] = \pi/4$ (see [[https://en.wikipedia.org/wiki/Monte_Carlo_method]["Monte Carlo +method" on Wikipedia]]). The following code uses this approach - -#+BEGIN_SRC R :session *R* :results output graphics :file "./pi.png" :exports both :width 600 :height 400 +#+begin_src R :session *R* :results output graphics :file "./pi.png" :exports both :width 600 :height 400 set.seed(42) N = 1000 df = data.frame(X = runif(N), Y = runif(N)) @@ -45,7 +44,7 @@ ggplot(df, aes(x=X,y=Y,color=Accept)) + geom_point(alpha=.2) + coord_fixed() + theme_bw() -#+END_SRC +#+end_src #+RESULTS: [[file:./pi.png]] @@ -54,9 +53,9 @@ It is then straightforward to obtain a (not really good) approximation to $\pi$ by counting how many times, on average, $X^2 + Y^2$ is smaller than 1: -#+BEGIN_SRC R :session *R* :results output :exports both +#+begin_src R :session *R* :results output :exports both 4*mean(df$Accept) -#+END_SRC +#+end_src #+RESULTS: : [1] 3.156 -- 2.18.1