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Integrating factors

  1. Sep 4, 2005 #1
    how do you spot that a D.E. needs an integrating factor, besides experience?
     
  2. jcsd
  3. Sep 5, 2005 #2

    Zurtex

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    If you're talking about 1st order O.D.Es, it's if you can get it of the form:

    [tex]\frac{dy}{dx} + Py = Q[/tex]

    Where P and Q are functions of x.
     
  4. Sep 5, 2005 #3
    thanks! :)
     
  5. Sep 6, 2005 #4

    HallsofIvy

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    If it's not already exact, it needs an integrating factor!

    The hard part is finding that integrating factor.
     
  6. Dec 27, 2005 #5

    mathwonk

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    it is just an extension of integration by parts, i.e. trying to use the product rule. "there are no new ideas under the sun".
     
  7. Dec 28, 2005 #6

    HallsofIvy

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    I'm not sure what you mean by "needs" an integrating factor. Every first order differential equation has an integrating factor but it may be very difficult to find. That's what I meant when I said before "If it's not already exact, it needs an integrating factor!"

    If a first order differential equation is linear then there is a simple formula for the integrating factor. I presume that was what Zurtex meant.
     
  8. Dec 28, 2005 #7
    thank you!!!
     
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