How to separate variables in this PDE?

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Discussion Overview

The discussion revolves around the separation of variables in a partial differential equation (PDE) of the form F,x,t + A(x)*F(x,t)*[(x+t)^(-3/2)] = 0, where A(x) is a known function of x. Participants are exploring methods to express the solution F(x,t) in a separable form, discussing various approaches and challenges encountered in the process.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant proposes separating F(x,t) into the form F1(x)*F2(t)*F3(x+t) but expresses frustration in finding a solution.
  • Another suggests a change of variables to (\zeta, \eta) = (x, x + t) and introduces an Ansatz F = H(\eta)Z(\zeta), leading to a new equation that they are uncertain can be separated.
  • A participant acknowledges trying a similar approach but remains unsure about the next steps in solving the equation.
  • There is a request for clearer notation, with a participant suggesting the use of LaTeX for better readability.
  • Clarification is provided regarding the notation F_{,x,t}, which denotes the mixed partial derivative of F with respect to x and t.
  • Another participant expresses surprise at the notation involving commas, indicating a lack of familiarity with it.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the separability of the equation or the best approach to take, indicating that multiple competing views and uncertainties remain in the discussion.

Contextual Notes

Participants mention that A(x) is a known but complex function, and there are unresolved steps in the mathematical reasoning regarding the separation of variables.

BB711
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TL;DR
Can anyone suggest a way to separate the variables in this PDE, so I can solve it analytically?
My PDE:
F,x,t + A(x)*F(x,t)*[(x+t)^(-3/2)] = 0

A(x) is a known function of x.
Trying to separate F(x,t) like
F(x,t) = F1(x)*F2(t)*F3(x+t).

I’m getting desperate to solve,
any suggestions??
 
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Make the change of variable (\zeta, \eta) = (x, x + t). Then the Ansatz F = H(\eta)Z(\zeta) yields <br /> H&#039;(\eta)Z&#039;(\zeta) + H&#039;&#039;(\eta)Z(\zeta) + A(\zeta)H(\eta)Z(\zeta)\eta^{-3/2} = 0. I'm not sure this is separable.
 
Thanks pasmith,
I did try something like that, and basically got that same type of equation, but I’m not sure what to do with it next. Still searching…
 
It wwould surely be easier to parse in ##LaTeX##
 
F_{,x,t} + \frac{A(x)}{(x+t)^{3/2}} F(x,t) = 0

A(x) is messy but known; F(x,t) must be solved for analytically, through separability or any other way.
 
Last edited:
What is ##F_{,x,t} ##?
 
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Common notation, F_{,x,t} \equiv \frac{\partial ^{2} F(x,t)}{\partial x \partial t}
 
Wow I've never seen it with the commas. OK thanks.
 
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