Nonlinear differential equation problem.

In summary, the conversation discusses a nonlinear equation that turned up while trying to make an integral stationary in a 'calculus of variations' problem. Equations of this type can be solved by using the identity y'' = y' (dy'/dy) and integrating both sides.
  • #1
center o bass
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2

Homework Statement


The following equation turned up while I was trying to make an integral
stationary in a 'calculus of variations' problem.

[tex]y^{\prime}(x)^2 + 1 = y^{\prime\prime}(x) y(x)[/tex]

How would one go about solving this nonlinear equation?
 
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  • #2
Equations like this, which do not contain the independent variable (x), can be solved by applying the identity:
[tex] y'' = \frac{d^2y}{dx^2} = \frac{dy'}{dx} = \frac{dy'}{dy}\frac{dy}{dx} = y' \frac{dy'}{dy}[/tex]
Then you can write:
[tex]y'^2+1 = y' \frac{dy'}{dy} y[/tex]
Then you collect terms in y and y' to get to a form you can integrate:
[tex] \frac{y' dy'}{1+y'^2} = \frac{dy}{y}[/tex]
Then integrate both sides and solve for y' in terms of y, and then integrate a second time.
 

Related to Nonlinear differential equation problem.

1. What is a nonlinear differential equation?

A nonlinear differential equation is a mathematical equation that involves an unknown function and its derivatives, where the function appears in a nonlinear way. This means that the function and its derivatives are not simply multiplied or divided by constants, but can also be raised to powers or have other functions applied to them.

2. What is the difference between linear and nonlinear differential equations?

The main difference between linear and nonlinear differential equations is that linear equations have a linear relationship between the dependent variable and its derivatives, while nonlinear equations have a nonlinear relationship. This means that linear equations can be solved using well-known techniques, such as separation of variables, while nonlinear equations often require more advanced methods.

3. Why are nonlinear differential equations important?

Nonlinear differential equations are important in many areas of science and engineering, as they can model complex and nonlinear phenomena that cannot be described by linear equations. They are also used to study systems that exhibit chaotic behavior, which is often found in natural systems like weather patterns and population dynamics.

4. What are some common methods for solving nonlinear differential equations?

Some common methods for solving nonlinear differential equations include numerical methods, such as Euler's method and Runge-Kutta methods, and analytical methods, such as perturbation methods and the method of series solutions. Additionally, computer software, such as Mathematica and MATLAB, can also be used to solve nonlinear differential equations.

5. Are there any real-life applications of nonlinear differential equations?

Yes, there are many real-life applications of nonlinear differential equations. Some examples include modeling chemical reactions, population growth and decline, electrical circuits, and fluid dynamics. They are also used in fields such as economics, biology, and ecology to study complex systems and phenomena.

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