# 21. Boundary Value Problems 2 | Summary and Q&A

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August 17, 2017
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MIT OpenCourseWare
21. Boundary Value Problems 2

## TL;DR

Galerkin methods use local basis functions to solve mathematical equations and optimize the values of coefficients (d's) to minimize the residual error.

## Key Insights

• ❓ Galerkin methods involve using local basis functions that are only nonzero in specific regions, resulting in sparse Jacobian matrices.
• ❓ The coefficients in the basis functions are adjusted to minimize the error between the approximate and true solutions.
• ❓ Galerkin methods are computationally efficient due to the sparsity of the Jacobian matrix.
• 😃 Local basis functions, such as b-splines, are commonly used in Galerkin methods.

## Transcript

The following content is provided under a Creative Commons license. Your support will help MIT OpenCourseWare continue to offer high quality educational resources for free. To make a donation or to view additional materials from hundreds of MIT courses, visit MIT OpenCourseWare at ocw.mit.edu. PROFESSOR: So today we're going to keep talking about b... Read More

### Q: What are Galerkin methods and how do they work?

Galerkin methods are numerical analysis techniques that involve using local basis functions for solving mathematical equations. The basis functions are adjusted to minimize the error between the approximate solution and the true solution.

### Q: What is the advantage of using local basis functions in Galerkin methods?

Local basis functions, such as b-splines, are only nonzero in specific regions, making the Jacobian matrix sparse. This sparsity reduces the computational complexity of solving the problem.

### Q: How are the coefficients in the basis functions adjusted in Galerkin methods?

The coefficients (d's) in the basis functions are adjusted to minimize the error between the approximate solution and the true solution. This is done by solving a system of equations, where the objective is to make the residual error equal to zero.

### Q: What is the role of the Jacobian matrix in Galerkin methods?

The Jacobian matrix represents the derivative of the residual function with respect to the coefficients (d's) in the basis functions. It helps in solving the system of equations by providing information about how changing the coefficients affects the error.

## Summary & Key Takeaways

• Galerkin methods involve using local basis functions that are nonzero only in specific regions for solving mathematical equations.

• The coefficients (d's) in the basis functions are adjusted to minimize the error between the approximation and the true solution.

• The Jacobian matrix in Galerkin methods is sparse, which means that most of the elements are zero, making the problem computationally efficient.