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Very interesting problem

  1. Aug 17, 2010 #1
    I have spent hours and hours trying to solve a problem until reaching a dead point. I don't know how to solve, simplify, or proceed next with the following PDE:

    [tex]m \frac{\partial^2 x}{\partial t^2} + 2 \frac{\partial m}{\partial t} \frac{\partial x}{\partial t} + x \frac{\partial^2 m}{\partial t^2}=0[/tex]

    Or, in other words: mx_tt + 2m_tx_t + xm_tt = 0

    [tex]m x_{tt} + 2 m_{t} x_{t} + x m_{tt}[/tex]

    I thought it'd be easier but I don't seem to be able to simplify it. Maybe it is a form I don't recognize.

  2. jcsd
  3. Aug 17, 2010 #2


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    What are you trying to solve for? x and m are both unknown functions?
  4. Aug 17, 2010 #3
    Your equation can be written as:

    [tex]\frac{\partial ^2(m x)}{\partial t^2}=0[/tex]

    And this can be solved easily. Hope it helps you.
  5. Aug 18, 2010 #4

    It helped me solve the differential equation, and it also made me realize that the solution is not what I expected it to be. I believe I need to revisit the formulation.

    Thanks again,

  6. Sep 5, 2010 #5
    You are welcome. Update us with your problem if you want.
  7. Sep 5, 2010 #6
    I've ended up with a variable coefficient wave equation, so I'm browsing for numerical solutions of similar problems at ScienceDirect.

    A closed form solution at this point is like asking Santa Claus for Dominion Over the Universe (yeah, um... not gonna happen).

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