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Alter the program MonteCarlo to estimate the area under the graph of \(y=\sin \pi x\) inside the unit square by choosing 10,000 points at random. Now calculate the true value of this area and use your results to estimate the value of \(\pi\). How accurate is your estimate?

Short Answer

Expert verified
Using Monte Carlo, the estimated area is \( \text{Estimated Area} \), which gives \( \pi_{estimate} \approx \frac{2}{\text{Estimated Area}} \). The accuracy is determined by the percentage error between \( \pi_{estimate} \) and \( \pi_{true} \).

Step by step solution

01

Understand the Function and the Problem

The function we are considering is \( y = \sin(\pi x) \). Our task is to estimate the area under this curve from 0 to 1 within the unit square by using 10,000 random points. This is done using the Monte Carlo method.
02

Setup of the Monte Carlo Simulation

We need to randomly generate 10,000 points within the unit square (0,0) to (1,1). For each random point \((x, y)\), we check if it falls below the curve \( y = \sin(\pi x) \). If \( y < \sin(\pi x) \), the point is considered to be "under" the curve.
03

Count Points Under the Curve

Count the number of points that fall under the curve \( y = \sin(\pi x) \). Let this be \( N_{under} \). This count helps in estimating the area under the curve.
04

Calculate Estimated Area

The estimated area under the curve is calculated using the ratio of points under the curve to the total number of points, given by \( \text{Estimated Area} = \frac{N_{under}}{N_{total}} \times \text{Area of the square} \). Since the area of the unit square is 1, it simplifies to \( \frac{N_{under}}{10000} \).
05

Calculate True Area under the Curve

The exact area under the curve \( y = \sin(\pi x) \) from 0 to 1 can be calculated using integration: \( \int_0^1 \sin(\pi x) \,dx = \left[-\frac{1}{\pi} \cos(\pi x)\right]_0^1 = \frac{2}{\pi} \).
06

Estimating \( \pi \)

Since the true area \( A = \frac{2}{\pi} \), you can estimate \( \pi \) using the formula \( \pi_{estimate} = \frac{2}{\text{Estimated Area}} \).
07

Evaluate Accuracy

Calculate the percentage error in the estimation of \( \pi \) using \( \frac{|\pi_{true} - \pi_{estimate}|}{\pi_{true}} \times 100\% \), where \( \pi_{true} = 3.141593 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Area Under a Curve
The area under a curve is a fundamental concept in calculus, often representing the total quantity's accumulation, such as distance, from a rate function like velocity. In this exercise, we calculate the area under the curve of the function \( y = \sin(\pi x) \) from \( x = 0 \) to \( x = 1 \). The area is estimated to understand how closely a function approximates reality when integrated over an interval. Using the Monte Carlo simulation method, this area is approximated by randomly selecting points in a unit square and determining what portion of them falls below the curve. This helps determine the approximate area quantitatively when dealing with complex shapes or functions where traditional methods might be cumbersome or impossible.
Random Sampling
Random sampling is a crucial technique used in Monte Carlo simulations to estimate numerical solutions to problems. By randomly selecting inputs (or sampling points) within a specified domain, we can simulate what occurs in a real-world scenario. In our problem, we chose 10,000 random points within the unit square that extends from (0,0) to (1,1). Each point consists of an \( x \) and \( y \) coordinate generated randomly.
  • For each point, \( x \) falls between 0 and 1.
  • For each point \( y \), we check if it's less than \( \sin(\pi x) \).
This randomness is essential because it ensures an unbiased sampling distribution across the interval, leading to a more accurate estimate of the area or integral we're calculating. By increasing the number of sampled points, we can potentially achieve greater accuracy.
Numerical Integration
Numerical integration involves approximating the value of an integral, often when a function does not have an elementary antiderivative or is too complex to integrate analytically. In the Monte Carlo method, we use random sampling for this purpose, circumventing traditional analytical methods.In the exercise, Monte Carlo integration allows us to estimate the integral of \( y = \sin(\pi x) \) from 0 to 1 by using the fraction of points that lie under the curve out of all sampled points. The more points sampled, the closer the approximation will be to the true integral. The simplicity and power of this method make it suitable for various complex integration problems across different fields, such as physics, finance, and engineering.
Accuracy Assessment
Assessing the accuracy of Monte Carlo simulations is crucial to ensure the reliability of results. In the problem given, we compare the estimated value of \( \pi \) based on our simulation against its true value \( \pi_{true} = 3.141593 \). The accuracy is checked by:
  • Calculating the percentage error using \( \frac{|\pi_{true} - \pi_{estimate}|}{\pi_{true}} \times 100\% \).
The error percentage tells us how close our approximation is to the true value. A smaller error percentage signifies a more reliable estimate. Various factors can affect accuracy, including the number of random points used and the inherent variability in random sampling. Therefore, understanding and assessing accuracy is essential for confirming the validity of simulation results.

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