My computer tells me that $\pi$ is *approximatively*
Asking the maths library
# On the computation of pi
*Arnaud Legrand*
*25 juin 2018*
## Asking the maths library
My computer tells me that π is approximatively
{r}
```{r}
pi
```
Buffon's needle
## Buffon's needle
Applying the method of Buffon's needle, we get the approximation
Applying the method of [Buffon's needle](https://en.wikipedia.org/wiki/Buffon%27s_needle_problem), we get the approximation
{r}
```{r}
set.seed(42)
N = 100000
x = runif(N)
theta = pi/2*runif(N)
2/(mean(x+sin(theta)>1))
```
Using a surface fraction argument
## 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]=π/4 (see "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 $P[X^2+Y^2\leq 1] = \pi/4$ (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 π by counting how many times, on average, X2 + Y2 is smaller than 1
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