Verifying Galilean Invariance of the KdV Equation

In summary, the KdV equation, ut + 6uux + uxxx = 0, is invariant under the Galilean transformation xi = x - ct, tau = t, and psi = phi - c/6. This means that changing variables in the KdV equation using the chain rule will result in the same equation. Therefore, proving the Galilean invariance of the KdV equation involves showing that the transformed equation is equivalent to the original one.
  • #1
squenshl
479
4

Homework Statement


Show that the KdV has Galilean invariance.
That is ut + 6uux + uxxx = 0 is invariant under the transformation xi = x - ct, tau = t, psi = phi - c/6


Homework Equations





The Attempt at a Solution


Do we use the chain rule on these and plug into the KdV?
 
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  • #2
That would be what I would do. Essentially you just want to make that "change" of variables and show that you get exactly the same equation again. And changing variables in a differential equation involves the chain rule.
 
  • #3
Thanks.
So d/dx = xix*d/dxi + taux*d/dtau = d/dxi
and d/dt = xit*d/dxi + taut*d/dtau = -cd/dxi + d/dtau
 
  • #4
Got it.
Thanks.
 

Related to Verifying Galilean Invariance of the KdV Equation

1. What is the KdV equation?

The Korteweg-de Vries (KdV) equation is a nonlinear partial differential equation that describes the propagation of long, weakly nonlinear waves in certain physical systems, such as shallow water waves or long internal waves in the ocean. It was first derived by Dutch mathematician Diederik Korteweg and physicist Gustav de Vries in 1895.

2. What does it mean for the KdV equation to be Galilean invariant?

Galilean invariance refers to the property of a physical system to remain unchanged under a Galilean transformation, which is a mathematical transformation that shifts the coordinate system by a constant velocity. In the context of the KdV equation, this means that the equation will still hold true even if the reference frame is moving at a constant velocity.

3. How is the Galilean invariance of the KdV equation verified?

The Galilean invariance of the KdV equation can be verified by performing a Galilean transformation on the equation and showing that it remains unchanged. This can be done mathematically by substituting the transformed variables into the equation and simplifying to show that it is still valid.

4. Why is it important to verify the Galilean invariance of the KdV equation?

Verifying the Galilean invariance of the KdV equation is important because it ensures that the equation accurately describes physical systems in different reference frames. This is crucial in many areas of science, such as fluid dynamics and oceanography, where the movement of objects or waves may be observed from different perspectives.

5. What are the implications of the KdV equation being Galilean invariant?

The Galilean invariance of the KdV equation has significant implications in the study of fluid dynamics and wave phenomena. It allows scientists to accurately describe and predict the behavior of waves in different reference frames, which has practical applications in fields such as engineering and oceanography.

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