What does the geodesic equation for a surface involve?

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Discussion Overview

The discussion revolves around the geodesic equation for a surface defined by the function z=f(x,y), specifically focusing on the form of the equation y=y(x) and the implications of its terms, including derivatives and mixed differentials.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant expresses confusion regarding the geodesic equation, particularly the presence of terms involving derivatives and mixed differentials.
  • Another participant questions the origin of the equation, suggesting it should derive from a tensor equation involving Christoffel symbols.
  • A participant clarifies that the equation is a special case for surfaces where z=f(x,y) and cites a specific source for this formulation.
  • There is a request for alternative sources for the equation, indicating difficulty in accessing the original reference.
  • One participant proposes that a term in the equation is likely a typographical error, suggesting it should refer to a first-order derivative instead.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the equation or its derivation, and there are competing views regarding the interpretation of its terms.

Contextual Notes

There are unresolved questions about the accuracy of the equation and the definitions of the terms involved, as well as the dependency on the specific source material referenced.

kleinwolf
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I don't understand the equation of the geodesic y=y(x) for the surface given by z=f(x,y) :

[tex]a(x)y''(x)=b(x)y'(x)^3+c(x)y'(x)^2+d(x)dxdy-e(x)[/tex]

the functions a,b,c,d,e are here not very important, what I don't understand, is that there is terms in [tex]\frac{dy}{dx}[/tex] and [tex]dxdy[/tex]...What does this mean ?
 
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Where did you get that equation...?It should come from the tensor one involving Christoffel symbols.

Daniel.
 
This is the equation in the special case where z=f(x,y)...the geodesics being given in the direct form : y=y(x)...I got this in Bronstein Taschenbuch der Mathematik.
 
I'm sorry,i can't get that book.Could u please indicate other source (it would be sizzling,if online) ?

Daniel.
 
Here is a scan :
 

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It's a typo,i'm sure the German dude meant the derivative of the first order

[tex]\frac{dy}{dx}[/tex].

Daniel.
 

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