Geometrical interpretation of this property

Click For Summary
SUMMARY

The discussion centers on the geometrical interpretation of a property related to ordinary differential equations (ODEs). Specifically, if x(t) is a solution to the system defined by \(\dot{x} = f(x)\) with initial condition \(x(t_0) = x_0\), then the function \(y(t) = x(t+t_0)\) also serves as a solution with initial condition \(y(0) = x_0\). The vector field f is visualized as a fluid's velocity, where the trajectory of a pebble dropped into this fluid represents the solution's path. The discussion concludes that the trajectories of x and y are identical but time-shifted, indicating that if the velocity is constant, both functions exhibit linear behavior with parallel graphs.

PREREQUISITES
  • Understanding of ordinary differential equations (ODEs)
  • Familiarity with vector fields and their geometrical interpretations
  • Knowledge of initial value problems in mathematics
  • Basic concepts of fluid dynamics and motion
NEXT STEPS
  • Explore the properties of solutions to ordinary differential equations (ODEs)
  • Study the concept of vector fields in mathematical physics
  • Learn about initial value problems and their significance in ODEs
  • Investigate the relationship between fluid dynamics and differential equations
USEFUL FOR

Mathematicians, physicists, and engineering students interested in the geometrical interpretation of differential equations and their applications in fluid dynamics.

brunob
Messages
15
Reaction score
0
Hi there!

I have the following property:
If x(t) is a solution of \left\{ \begin{array}{l} \dot{x} = f(x) \\ x(t_0) = x_0 \end{array} \right. then the function y(t) = x(t+t_0) is a solution of the equation with initial data y(0) = x_0.

How could it be interpreted geometrically?
Thanks!
 
Physics news on Phys.org
Geometrically, think of f as a vector field. Imagine it as a collection of arrows describing the velocity of a fluid; that is, for each x, f(x) is the velocity of the fluid at the point x.

Now, imagine a small pebble moving in this fluid. At each point x, the trajectory of the pebble must be tangent to the vector f(x) (why?). Dropping a pebble into the fluid at a specific point x_0 represents an initial condition of your ODE. The answer to your question is the following: it doesn't matter what time you drop the pebble at x_0; the pebble's resulting trajectory will always be the same, because the fluid velocity field is unchanging with time.

The image of the solution of y is just a copy of the image of x, but shifted in time -- just like the pebble's motion when dropped at time t_0 is identical to its motion when dropped at 0, but shifted in time.
 
Nice example! So, if the velocity is constant it means that the position x(t) is linear and so y(t) is, and due the way the functions are linked I can say that their graphics are parallels.
Let me know if I'm wrong.

Thanks!
 

Similar threads

  • · Replies 0 ·
Replies
0
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 65 ·
3
Replies
65
Views
8K