# Buffons needle a simple monte carlo method for the estimation of the value of pi

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The distance from the center to the closest line can never be more that half the distance between the lines. This phenomenon is sometimes given the funny descriptive name of "Buffon's Noodle!

Further down, you can also change the scale of the needles dropped or restart the experiment from the beginning.

### A needle of length l is dropped at random onto a sheet of paper

However, it is somewhat counterintuitive to think that flipping the coin millions, billions or trillions of times could give us insight into what is happening in a nuclear reactor, into tomorrow's weather, or into our current recession. We can look at this graphically. A good discussion of these can be found in Schroeder , The diagram on the left shows an example of this using unit floating point coordinates, but the method works with quantized fixed coordinates too such as those that could be generated by the roll of a die. Some consider LeClerc's experiment the first instance of Monte Carlo simulation. If you threw a piece of wet spaghetti neglecting the fact that, if it overlapped, it's not quite in the same plane , and counted the overlaps it would be the same overlap percentage as a piece of dry spaghetti of the same length. It involves dropping a needle on a lined sheet of paper and determining the probability of the needle crossing one of the lines on the page. Results and Discussions A series of experiments were performed using this program. The ratio of the points that fall inside the circle compared to all point should be the same as the ratio of the area of circle to the area of the square.

The Simplest Case Let's take the simple case first. We can throw both of these half-length needles on the floor.

What is the probability that the needle falls such that it lies over a crack? Then, we get a number of ordered his money Metropolis, Let m be the number of such points. The Other Cases There are two other possibilities for the relationship between the length of the needles and the distance between the lines.

The Central Limit Theorem will smooth out the answers. That's approximately.

## Buffons noodle

We can prove this with a thought experiment: Imagine we have a needle of length one unit and cut it in half to make two needles of length half a unit each. The simulation can be started and stopped using the button in the lower left. This method is an pairs x, y , each of which represent a point on the outgrowth of the Law of Large Numbers, which states coordinate axis. Since the needle is dropped entirely at random, the position can be described by two independent variables. This is a bit of a handful, so to simplify if we define the ratio of the length of the needle to the width of the board to be x normalize it , we get a slightly simpler equation: Plotting this on a graph where the x-axis shows the normalized ratio x and the y-axis shows the probability, we get the following curve: When the needle is "short", the probability linearly changes with the ratio of the length more on this later. The distance from the center to the closest line can never be more that half the distance between the lines. There are four speeds that can toggled between. The needle in the picture misses the line. Generic Solution The above solution was for the simple case of dropping a needle the same length as the separation between the lines.

Whether the two halves are connected, or not, does not matter and if they are connected, it does not matter the angle between the two halves.

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