Commit f4ae8d30 authored by Jhouben's avatar Jhouben

Update toy_document_en.Rmd

parent 7cd7245d
......@@ -5,7 +5,6 @@ date: "20/05/2021"
output: html_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
......@@ -15,7 +14,8 @@ My computer tells me that $\pi$ is *approximatively*
```{r}
pi
```
```
## Buffon's needle
Applying the method of [Buffon's needle](https://en.wikipedia.org/wiki/Buffon%27s_needle_problem), we get the __approximation__
......@@ -27,7 +27,6 @@ theta = pi/2*runif(N)
2/(mean(x+sin(theta)>1))
```
## 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 $P[X^2+Y^2\leq 1] = \pi/4$ (see ["Monte Carlo method" on Wikipedia](https://en.wikipedia.org/wiki/Monte_Carlo_method)). The following code uses this approach:
......@@ -38,10 +37,11 @@ df = data.frame(X = runif(N), Y = runif(N))
df$Accept = (df$X**2 + df$Y**2 <=1)
library(ggplot2)
ggplot(df, aes(x=X,y=Y,color=Accept)) + geom_point(alpha=.2) + coord_fixed() + theme_bw()
```
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:
```{r}
4*mean(df$Accept)
```
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