# Boundary Conditions for System of PDEs

• I
• Mzzed
In summary, the conversation discusses the issue of choosing appropriate boundary conditions for a system of partial differential equations (PDEs) and specifically for a system of 4 PDEs describing plasma in a cylinder. The dependent and independent variables involved are also mentioned. The person asks for rules or guidelines for selecting boundaries for such a system and if the same rules for a single PDE apply. They also request any recommended sources for learning about boundary conditions for PDEs, such as a tutorial and a book by Boyce and Deprima.
Mzzed
I am unsure how to choose the boundary conditions for a system of PDEs or for a single PDE for that matter.

The situation I am stuck with involves a system of 4 PDEs describing plasma in a cylinder. The dependent variables being used are Vr, Vt, Vz, ni, and the independent variables are Rr, Ttheta, Zz (cylindrical coords). None of the partial differentials involved in any of these equations are above first order.

What are the rules/guide lines for choosing the boundarys for such a system of PDEs? Do the same rules for choosing boundarys of a single PDE still hold for a system of PDEs?

Also if you know of any good sources that specifically teach about the choice of boundary conditions for a PDE I would really appreciate it.

Thanks!

Mzzed

## 1. What are boundary conditions in a system of PDEs?

Boundary conditions in a system of PDEs refer to the set of conditions that must be satisfied at the boundaries of the domain in order for a unique solution to exist. They specify the behavior of the solution at the boundaries and are crucial for solving PDEs numerically or analytically.

## 2. Why are boundary conditions important in solving PDEs?

Boundary conditions are important because they help determine the unique solution to a system of PDEs. Without them, there may be an infinite number of possible solutions, making it impossible to find a specific solution that accurately describes the behavior of the system.

## 3. What are the types of boundary conditions in a system of PDEs?

There are several types of boundary conditions in PDEs, including Dirichlet, Neumann, and Robin boundary conditions. Dirichlet conditions specify the value of the solution at the boundary, while Neumann conditions specify the derivative of the solution at the boundary. Robin conditions are a combination of Dirichlet and Neumann conditions.

## 4. How are boundary conditions applied in numerical methods for solving PDEs?

In numerical methods, boundary conditions are applied by discretizing the domain into a grid and using finite difference or finite element methods to approximate the solution at the boundaries. The boundary conditions are then incorporated into the system of equations, allowing for the solution to be solved at each grid point.

## 5. Can boundary conditions change the behavior of the solution in a system of PDEs?

Yes, boundary conditions can significantly affect the behavior of the solution in a system of PDEs. For example, changing the boundary conditions from Dirichlet to Neumann can result in a completely different solution. It is important to carefully choose and apply appropriate boundary conditions to accurately describe the behavior of the system.

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