Separable partial differential equation

In summary: In general, the constant of integration you get by integrating over θ, can be a function of r , etc.In summary, the given conversation discusses two equations (1) and (2) and the task to find wφ as a function of both r and theta. The first equation is corrected to be cos(θ)wφ+sin(θ) ##\frac{∂w_φ}{dθ}=0## and the second equation is ##\frac{w_φ}{r}##+∂wφ/∂r = 0. After integrating, the solutions for wφ are ##\frac{A}{sinθ}## from (1) and Ar from (2), with A
  • #1
whatisreality
290
1

Homework Statement


I have two equations.
cos(θ)wφ + sin(θ)wφ = 0 (1)
And
## \frac{w_φ}{r}## + ∂wφ/∂r = 0 (2)
Find wφ, which is a function of both r and theta.

Homework Equations

The Attempt at a Solution


I end up with two equations, having integrated. wφ=## \frac{A}{sinθ}## from (1), and wφ = Ar from (2). A is a constant of integration.
Is A the same in both equations? How do I combine the two solutions into one? I don't think you add them.
 
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  • #2
whatisreality said:

Homework Statement


I have two equations.
cos(θ)wφ + sin(θ)wφ = 0 (1)
And
## \frac{w_φ}{r}## + ∂wφ/∂r = 0 (2)
Find wφ, which is a function of both r and theta.

Homework Equations

The Attempt at a Solution


I end up with two equations, having integrated. wφ=## \frac{A}{sinθ}## from (1), and wφ = Ar from (2). A is a constant of integration.
Is A the same in both equations? How do I combine the two solutions into one? I don't think you add them.

Have you typed the the first equation correct? Because if not [itex]w_φ=0[/itex], and for the rest: remember that when you differentiate / integrate with respect to [itex]r[/itex] you may have lost a function of θ.
 
  • #3
6c 6f 76 65 said:
Have you typed the the first equation correct? Because if not [itex]w_φ=0[/itex], and for the rest: remember that when you differentiate / integrate with respect to [itex]r[/itex] you may have lost a function of θ.
I know it isn't zero... But actually the first equation isn't correct, typed wrong.
Should be sin(θ) multiplied by the partial differential of wφ with respect to theta
 
  • #4
Did I differentiate instead of integrating? I checked the integration, can't find a mistake.
 
Last edited:
  • #5
whatisreality said:
I know it isn't zero... But actually the first equation isn't correct, typed wrong.
Should be sin(θ) multiplied by the partial differential of wφ with respect to theta
How about writing that first equation again in its corrected form, in its entirety .
 
  • #6
SammyS said:
How about writing that first equation again in its corrected form, in its entirety .
Sorry. Here it is:
cos(θ)wφ+sin(θ) ##\frac{∂w_φ}{dθ}=0##.
 
  • #7
OK.

For your question regarding the constant of integration, A .

You would not expect the two constants of integration to be the same.

In general, the constant of integration you get by integrating over θ, can be a function of r , etc.
 

1. What is a separable partial differential equation (PDE)?

A separable PDE is a type of differential equation that can be separated into individual equations for each of the variables involved. This allows for the solution to be found by solving each individual equation separately.

2. How is a separable PDE different from a non-separable PDE?

A non-separable PDE cannot be separated into individual equations for each variable and therefore requires more complex methods to solve. Separable PDEs are often easier to solve and have more readily available solutions.

3. What types of problems can be modeled using separable PDEs?

Separable PDEs are commonly used to model physical phenomena such as heat flow, fluid dynamics, and diffusion. They are also used in financial modeling and other fields that involve continuous change over multiple variables.

4. How do you solve a separable PDE?

To solve a separable PDE, the equation is first separated into individual equations for each variable. These equations are then solved separately using appropriate methods, such as integration or separation of variables. The solutions are then combined to find the overall solution to the PDE.

5. What are some common applications of separable PDEs in real-world problems?

Separable PDEs are commonly used in engineering and physics to model heat and mass transfer, fluid flow, and other physical processes. They are also used in economic and financial modeling to study population growth, resource allocation, and other systems that involve continuous change over multiple variables.

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