What is the General Solution to the Differential Equation?

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Discussion Overview

The discussion revolves around finding the general solution to the differential equation \(\frac{\partial X_x}{\partial t} = - \frac{\partial X_t}{\partial x}\). Participants explore the nature of the functions involved and the implications of the equation, including potential forms of solutions and the behavior of partial derivatives.

Discussion Character

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

Main Points Raised

  • One participant seeks the general solution to the differential equation and requests resources for further study.
  • Another participant questions the notation used, suggesting that \(X_x\) might refer to \(\frac{\partial X}{\partial x}\), leading to a discussion about the implications of Clairaut's theorem regarding the continuity of partial derivatives.
  • A participant proposes rewriting the equation in terms of two functions \(X\) and \(T\), indicating that they must be equal to a constant, though this assertion is met with requests for clarification.
  • There is a suggestion that the functions on either side of the equation may not be equal in general, prompting questions about the general forms of \(X\) and \(T\).
  • A later post provides a specific form of the solution, indicating that \(X\) can be expressed as \(X = f(t - x)\) for any differentiable function \(f\).
  • Another participant reiterates the rewriting of the equation and provides examples of functions \(X\) and \(T\), while expressing confusion about the claim that they must be equal to a constant.

Areas of Agreement / Disagreement

Participants express varying interpretations of the equation and its implications, with no consensus reached on the nature of the functions or the conditions under which they hold. Disagreements arise regarding the equality of the functions and the interpretation of their derivatives.

Contextual Notes

Some assumptions about the continuity of partial derivatives and the definitions of the functions involved remain unresolved, leading to differing interpretations of the equation's implications.

llorgos
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Hi! I would like to ask what is the general solution of the following differential equation
\frac{\partial X_x}{\partial t} = - \frac{\partial X_t}{\partial x}

Thank you very much.

P.S. If you have some good resiource about this tyoe of equation to recommend please do so.
 
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What is Xx - does that stand for \frac{\partial X}{\partial x} ?
Because then you are basically asking about X_{xt} = -X_{tx}.

In that case you should be looking at "weird" functions - given Clairaut's theorem at least the partial derivatives should not be continuous.
 
Hi.

If you want I can write it as \frac{\partial X}{\partial t} = -\frac{\partial T}{\partial x} where T = T(x,t) and X = X(x,t) in general.

I know they must be equal to a constant. Please correct me if I am wrong.

Thank you.
 
So the functions on the left and right hand side are not equal in general? And you're asking what the general form for X and T is as separate functions?
 
\frac{\partial X}{\partial t} = -\frac{\partial X}{\partial x}
X=f(t-x) any derivable function f
 
llorgos said:
Hi.

If you want I can write it as \frac{\partial X}{\partial t} = -\frac{\partial T}{\partial x} where T = T(x,t) and X = X(x,t) in general.

I know they must be equal to a constant. Please correct me if I am wrong.

Thank you.
Let X(x, t)= f(x, t) be any differentiable function of x and t and define T(x, t)= -f(t, x).
For example, take X(x, t)= x+ t^2, T(x, t)= -t- x^2. Then \partial X/\partial x= 1= -\partial T/\partial t.

I don't know what you mean by "they must be equal to a constant".
 

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