Why Can't the Graph of a First Order Autonomous ODE Cross a Critical Point?

In summary, the graph of a solution can never cross a critical point because once at a critical point, the equation is first order and will never move again. This can be traced "backwards" to explain why a solution starting away from critical points will never touch or cross one.
  • #1
Skrew
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Could someone explain why the graph of a solution can never cross a critical point?
 
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  • #2
OK, to be concrete, let x'=F(x), and let a critical point be xc such that F(xc)=0. Then, if for a given t, x(t)=xc, then x'(t)=F(xc)=0 and, since the equation is first order, it is never going to move again! So: once at a critical point, always at a critical point.

The same argument can be traced "backwards", and that explains why a solution starting away from critical points will never touch one. It may approach, but never touch, much less cross.
 

FAQ: Why Can't the Graph of a First Order Autonomous ODE Cross a Critical Point?

What is a first-order autonomous ODE?

A first-order autonomous ODE (Ordinary Differential Equation) is a mathematical equation that describes the relationship between a function and its derivative with respect to one independent variable. It is "first-order" because it contains only first derivatives, and "autonomous" because the independent variable does not appear explicitly in the equation.

What are some examples of first-order autonomous ODEs?

Some examples of first-order autonomous ODEs include the logistic equation, the damped harmonic oscillator, and the Lotka-Volterra predator-prey model. These equations are commonly used to model real-world phenomena in fields such as biology, physics, and economics.

How do you solve a first-order autonomous ODE?

The general solution to a first-order autonomous ODE can be found by using separation of variables, integrating both sides of the equation, and then solving for the function. However, in most cases, it is not possible to find an exact solution and numerical methods must be used to approximate the solution.

What are the applications of first-order autonomous ODEs?

First-order autonomous ODEs are used in a wide range of applications, including population dynamics, chemical reactions, and electrical circuits. They are also important in control theory, which is used to design systems that can maintain stability and achieve a desired output.

What is the significance of first-order autonomous ODEs in science?

First-order autonomous ODEs are fundamental tools in scientific research, as they allow us to describe and understand complex systems and phenomena. They are also important for developing mathematical models and simulations, which can help predict and analyze the behavior of these systems.

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