Second order nonlinear ODE - not autonomous

In summary, the conversation discusses a second order nonlinear ordinary differential equation that arises from a steady state problem of diffusion with nonlinear reaction. The equation can be written as y''-k_0-(k_1+k_3 x)y-k_2 y^2=0 and a solution can be obtained by dropping the last term involving the product of the dependent and independent variable. However, the question is whether there is a way to obtain a solution with this term included. Two possible approaches are suggested: computing the solution numerically and fitting the data to a polynomial, or using a power series with a convergence radius of one. The conversation also mentions that this equation is not found in the Handbook of DEs, another book on nonlinear equations,
  • #1
Prof_Hydro
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second order nonlinear ODE -- not autonomous

This equation has arisen from a steady state problem of diffusion with nonlinear reaction:

(dependent var=c; independent variable=x)

c'' = ko + k1 c + k2 c^2 + k3 c x

ko, etc are constants.

I can obtain a solution if I drop the last term which involves the product of the dependent and independent variable. Is there any way to get a solution with this term?
 
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  • #2


Hello Prof. Mind if I write it as:

[itex]y''-k_0-(k_1+k_3 x)y-k_2 y^2=0[/itex]

and if you wish an analytical expression for the solution, I suggest two options unless someone comes up with a better way:

(1) Compute an IVP numerically and fit the data to a high-degree polynomial within your range of acceptable error.

(2) Compute the power series [itex]y=\sum_{n=0}^{\infty} a_n x^n[/itex]

I realize there is a square in the power series approach but I would just take the Cauchy product. Would need to figure out the convergence radius of course which I suspect is no more than one. I recommend this approach for the following reasons: It's not in the Handbook of DEs, not in another book on non-linear ones, and Mathematica's DSolve can't solve it. Of course, that doesn't mean a nice way doesn't exists but rather I'm just out of bullets. :)
 
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Related to Second order nonlinear ODE - not autonomous

1. What is a second order nonlinear ODE?

A second order nonlinear ODE (ordinary differential equation) is a mathematical equation that involves a second derivative of a function, as well as nonlinear terms. It can describe a wide range of physical phenomena, such as fluid flow, chemical reactions, and population growth.

2. What does it mean for an ODE to be non-autonomous?

An ODE is considered non-autonomous if it depends explicitly on the independent variable. This means that the equation is not time-invariant and can change with respect to time. In other words, the equation has a time-varying coefficient.

3. How do you solve a second order nonlinear ODE?

Solving a second order nonlinear ODE can be a challenging task and often requires advanced mathematical techniques. Some common methods for solving these types of equations include power series solutions, numerical methods, and integrating factors. It is also important to check for any special cases or symmetries in the equation that may simplify the solution process.

4. What are some applications of second order nonlinear ODEs?

Second order nonlinear ODEs have many applications in science and engineering. For example, they can be used to model the motion of a pendulum, the behavior of electric circuits, and the growth of tumor cells. They are also commonly used in control systems and in the study of chaotic systems.

5. What are the differences between a linear and nonlinear ODE?

A linear ODE is one in which the dependent variable and its derivatives appear in linear combinations, while a nonlinear ODE contains nonlinear terms. This means that the coefficients in a linear ODE are constant, while in a nonlinear ODE, they may vary with respect to the independent variable. The solutions to linear ODEs are typically easier to find, while nonlinear ODEs can exhibit more complex and interesting behavior.

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