My computer tells me that $\pi$ is approximatively
## Asking the maths library
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**
## Buffon's needle
Applying the method of [Buffon's needle](https://en.wikipedia.org/wiki/Buffon%27s_needle_problem), we get the __approximation__
```{r}
set.seed(42)
...
...
@@ -28,8 +27,8 @@ 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 $X∼U(0,1)$ and $Y∼U(0,1)$, then $P[X2+Y2≤1]=\pi/4$ (see [“Monte Carlo method” on Wikipedia](https://en.wikipedia.org/wiki/Monte_Carlo_method)). The following code uses this approach:
## 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 $P[X2+Y2\leq 1]= \pi/4$ (see ["Monte Carlo method" on Wikipedia](https://en.wikipedia.org/wiki/Monte_Carlo_method)). The following code uses this approach:
It is therefore 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 :
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 :