Tensor equations / nonlinear transformationsby JustinLevy Tags: equations, nonlinear, tensor, transformations 

#1
Apr1906, 04:51 AM

P: 886

I have some fairly basic (hopefully) questions about tensor equations. Hopefully someone here can help out.
Let us say I have a tensor equation, (I will use this as the example for discussion: [tex]A^{u} = b C^{uv}D_{v}[/tex]). If this is true in one coordinate system, it will be true in all of them correct? Now if I know the components of A,C,D in one frame (as well as the metric in this frame), then I can find the components of A,C,D in any other frame by transforming them, correct? Can I get the metric in this new frame by transforming the metric like a normal tensor as well (it does not seem to work in general... maybe I am making mistakes)? How do nonlinear transformations work? (For instance if I wanted to find A,C,D in an accelerated frame.) Since the transformation tensor just gives a linear transformation ... it seems to suggest that I need the metric to no longer be a constant in the frame!? Or does it work some other way? 



#2
Apr1906, 07:02 AM

Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 38,879

If A is the tensor in x,y coordinates and A' is the same tensor in x',y' coordinates, then
[tex]A'= \frac{\partial x'}{\partial x}\frac{\partial y'}{\partial y}A[/tex] That works for linear or nonlinear transformations. For a linear transformation the partial derivatives would be represented by a matrix having the coefficients as entries. For a nonlinear transformation, the entries in the matrix will be functions of position. 


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