Separable non-linear ODE (with radicals)











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I am trying to solve the equation



$$
frac{dy}{dt}=sqrt{(gamma-1+frac{2alphabeta}{2alpha-1})e^{-2alpha y}-frac{2alphabeta}{2alpha-1}e^{-y}+1}tag{1}
$$



$y(0) = 0$; $t_{0}=0$; $alpha$, $beta$ and $gamma$ are positive constants ($beta$ is also less than 1). There is also a special form for $alpha=frac{1}{2}$ but I will not dwell on this right now.



Provided I am not mistaken, letting $x = e^{-y}$ and rearranging leads to



$$
int_{e^{-y(t)}}^{1}{frac{dx}{xsqrt{(gamma-1+frac{2 alphabeta}{2alpha-1})x^{2alpha}-frac{2 alphabeta}{2alpha-1}x+1}}}=ttag{2}
$$



This integral is solvable for particular values of $alpha$ (ones that allow a partial fraction decomposition of the integrand(?))



My questions are:



1) Is there a relatively compact way that may determine if the
integral $(2)$ can be expressed in closed form?



2) Can $x(t)$ be expressed in terms of relatively well-studied special
functions?



3) Even if a general method for solving this equation (which I believe
does not exist), is there a way of obtaining an approximate solution
for $x(t)$ in closed form?



I have considered taking the Taylor series of the radical, but unfortunately this method does not work very well because the integrand does contain a region of rapid change within the integration region.



Any ideas on how to treat this problem will be greatly appreciated!










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    up vote
    8
    down vote

    favorite
    1












    I am trying to solve the equation



    $$
    frac{dy}{dt}=sqrt{(gamma-1+frac{2alphabeta}{2alpha-1})e^{-2alpha y}-frac{2alphabeta}{2alpha-1}e^{-y}+1}tag{1}
    $$



    $y(0) = 0$; $t_{0}=0$; $alpha$, $beta$ and $gamma$ are positive constants ($beta$ is also less than 1). There is also a special form for $alpha=frac{1}{2}$ but I will not dwell on this right now.



    Provided I am not mistaken, letting $x = e^{-y}$ and rearranging leads to



    $$
    int_{e^{-y(t)}}^{1}{frac{dx}{xsqrt{(gamma-1+frac{2 alphabeta}{2alpha-1})x^{2alpha}-frac{2 alphabeta}{2alpha-1}x+1}}}=ttag{2}
    $$



    This integral is solvable for particular values of $alpha$ (ones that allow a partial fraction decomposition of the integrand(?))



    My questions are:



    1) Is there a relatively compact way that may determine if the
    integral $(2)$ can be expressed in closed form?



    2) Can $x(t)$ be expressed in terms of relatively well-studied special
    functions?



    3) Even if a general method for solving this equation (which I believe
    does not exist), is there a way of obtaining an approximate solution
    for $x(t)$ in closed form?



    I have considered taking the Taylor series of the radical, but unfortunately this method does not work very well because the integrand does contain a region of rapid change within the integration region.



    Any ideas on how to treat this problem will be greatly appreciated!










    share|cite|improve this question


























      up vote
      8
      down vote

      favorite
      1









      up vote
      8
      down vote

      favorite
      1






      1





      I am trying to solve the equation



      $$
      frac{dy}{dt}=sqrt{(gamma-1+frac{2alphabeta}{2alpha-1})e^{-2alpha y}-frac{2alphabeta}{2alpha-1}e^{-y}+1}tag{1}
      $$



      $y(0) = 0$; $t_{0}=0$; $alpha$, $beta$ and $gamma$ are positive constants ($beta$ is also less than 1). There is also a special form for $alpha=frac{1}{2}$ but I will not dwell on this right now.



      Provided I am not mistaken, letting $x = e^{-y}$ and rearranging leads to



      $$
      int_{e^{-y(t)}}^{1}{frac{dx}{xsqrt{(gamma-1+frac{2 alphabeta}{2alpha-1})x^{2alpha}-frac{2 alphabeta}{2alpha-1}x+1}}}=ttag{2}
      $$



      This integral is solvable for particular values of $alpha$ (ones that allow a partial fraction decomposition of the integrand(?))



      My questions are:



      1) Is there a relatively compact way that may determine if the
      integral $(2)$ can be expressed in closed form?



      2) Can $x(t)$ be expressed in terms of relatively well-studied special
      functions?



      3) Even if a general method for solving this equation (which I believe
      does not exist), is there a way of obtaining an approximate solution
      for $x(t)$ in closed form?



      I have considered taking the Taylor series of the radical, but unfortunately this method does not work very well because the integrand does contain a region of rapid change within the integration region.



      Any ideas on how to treat this problem will be greatly appreciated!










      share|cite|improve this question















      I am trying to solve the equation



      $$
      frac{dy}{dt}=sqrt{(gamma-1+frac{2alphabeta}{2alpha-1})e^{-2alpha y}-frac{2alphabeta}{2alpha-1}e^{-y}+1}tag{1}
      $$



      $y(0) = 0$; $t_{0}=0$; $alpha$, $beta$ and $gamma$ are positive constants ($beta$ is also less than 1). There is also a special form for $alpha=frac{1}{2}$ but I will not dwell on this right now.



      Provided I am not mistaken, letting $x = e^{-y}$ and rearranging leads to



      $$
      int_{e^{-y(t)}}^{1}{frac{dx}{xsqrt{(gamma-1+frac{2 alphabeta}{2alpha-1})x^{2alpha}-frac{2 alphabeta}{2alpha-1}x+1}}}=ttag{2}
      $$



      This integral is solvable for particular values of $alpha$ (ones that allow a partial fraction decomposition of the integrand(?))



      My questions are:



      1) Is there a relatively compact way that may determine if the
      integral $(2)$ can be expressed in closed form?



      2) Can $x(t)$ be expressed in terms of relatively well-studied special
      functions?



      3) Even if a general method for solving this equation (which I believe
      does not exist), is there a way of obtaining an approximate solution
      for $x(t)$ in closed form?



      I have considered taking the Taylor series of the radical, but unfortunately this method does not work very well because the integrand does contain a region of rapid change within the integration region.



      Any ideas on how to treat this problem will be greatly appreciated!







      calculus integration differential-equations dynamical-systems






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      edited Nov 14 at 12:29









      amWhy

      191k27223437




      191k27223437










      asked Oct 20 '13 at 21:50









      JMK

      183119




      183119



























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