Really easy PDE, confused about how to put in side conditions

In summary, the conversation discusses finding the particular solution for a PDE with side conditions u(x,1) = 0 and u(0,y) = 0. The solution involves integrating with respect to x and y, and using an integrating factor. The final solution involves functions H(y) and k(x), but there is confusion about finding solutions for these functions on their own. The speaker eventually figures out a solution.
  • #1
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Hey, before you read this over I'll mention that I've checked the general solution and it works. So if you don't feel like following my steps to get the general solution just jump down to the end of my attempt, because the real problem for me is figuring out what to do with the side conditions.

Homework Statement


get the particular solution for this PDE, for side conditions u(x,1) = 0 ; u(0,y) = 0

yuxy + 2ux = x


Homework Equations


nothing really...


The Attempt at a Solution



first I integrate w.r.t x, which is suggested in the text:

yuy + 2u = x2/2 + h(y) ; where y is some function of y

divide through by y...

uy + 2u/y = x2/2y + h(y)/y

now take integrating factor y2 (I think this next line follows obviously, if it is confusing please let me know and I'll show you how I got it):

y2u = (x2y2)/4 + ∫h(y)ydy + k(x)

at this point I have done the integral with respect to y on each side, basically. so some function k(x) shows up. Now I replace ∫h(y)ydy with just H(y), some new function of y because the whole expression ∫h(y)ydy will end up being only dependent on y so we just rename the thing:

y2u = (x2y2)/4 + H(y) + k(x)

and divide through by y2...

u = (x2)/4 + H(y)/(y2)+ k(x)/(y2)

so here's where I get confused: if I put u(x,1) into the general solution I get:
k(x) = -x2/4 - H(1)

and for u(0,y) I get:

H(y) = -k(0)

But I see no way of getting solutions for k(x) and H(y) on their own. Is there something I'm missing here? Some sort of "trick" or other thing I should be aware of? Thanks for any advice.
 
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  • #2
aaaand just got it.
 

Related to Really easy PDE, confused about how to put in side conditions

1. What exactly are side conditions in PDEs?

Side conditions, also known as boundary conditions, are additional information or constraints that are imposed on a partial differential equation (PDE) to help determine a unique solution. They specify the behavior of the solution at the boundaries or edges of the domain in which the PDE is being solved.

2. How do I know which side conditions to use for a particular PDE?

The choice of side conditions depends on the physical problem being modeled by the PDE. Generally, physical principles such as conservation laws or the behavior of the system at its boundaries can guide the selection of appropriate side conditions. It is important to carefully consider the physical meaning of the problem and choose side conditions that reflect this understanding.

3. Can I use different types of side conditions for a single PDE?

In most cases, a PDE will require a consistent set of side conditions to find a unique solution. However, there are some PDEs that allow for different types of side conditions to be used together. This is often the case for more complex systems or when modeling different physical phenomena within the same PDE. It is important to carefully analyze the PDE and determine if multiple types of side conditions can be used together.

4. How do I incorporate side conditions into the PDE when solving it numerically?

When solving a PDE numerically, the side conditions are typically incorporated into the discretization process. This can be done by using finite difference, finite element, or other numerical methods that allow for the inclusion of boundary conditions. It is important to carefully code and implement the side conditions to ensure accurate solutions.

5. What happens if I don't include side conditions in my PDE solution?

If no side conditions are included in the PDE solution, the solution will most likely not be unique. This means that there will be multiple possible solutions that satisfy the PDE, which is not physically meaningful. The inclusion of side conditions is crucial for obtaining a unique and physically meaningful solution to a PDE.

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