- #1
Stalker_VT
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Homework Statement
I am trying to solve the transport PDE using a change of variables and the chain rule, and my problem seems to be with the chain rule. The PDE is:
[itex]\frac{\partial u}{\partial t}[/itex]+c[itex]\frac{\partial u}{\partial x}[/itex] = 0 ......(1)
The change of variables (change of reference frame) is:
[itex]\xi[/itex] = x - ct......(2)
From this we know that
u(t,x) = v(t, x - ct) = v(t, [itex]\xi[/itex])......(3)
The Attempt at a Solution
Taking the total derivative of both sides of (3)
[itex]\frac{d}{dt}[/itex] [u(t,x) = v(t,[itex]\xi[/itex])]
using chain rule yields
[itex]\frac{\partial u}{\partial t}[/itex] = [itex]\frac{\partial v}{\partial t}[/itex] - c[itex]\frac{\partial u}{\partial x}[/itex]......(4)
I think the next step is to PROVE that
[itex]\frac{\partial u}{\partial x}[/itex] = [itex]\frac{\partial v}{\partial \xi}[/itex].....(5)
and then substitute (4) into (5) to get
[itex]\frac{\partial v}{\partial t}[/itex] = 0
but i am not sure how to do this...Any help Greatly Appreciated
Thanks!
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