Wednesday, 2 December 2015

Calculate Tensor and its transformations, transformation of derivatives of dependent variables


I had been learning tensor notation for a while and here's what's I have read:


1 Tensor had rank, denote two types covarient or contravariant.


2 T(_α,_β,_γ) in place naming notion was =Tijkeiejek(_α,_β,_γ).


3 Quote from modern classical physics: When doing tensor calculus, coefficient Tijk never changes, what changed was the bases i.e. T=Tijkeiejek and Tijk=T(ei,ej,ek) so Tijk abbreviates for T in terms of ei,ej,ek; and transformation Tαβγ=Tijkgiαgjβgkγ.


4 Each tensor could be written as combination of asymmetry and symmetry parts.


5 Aij=xixlxmxjAlm so gil=xixl and gmj=xmxj.


Question 1: However, I did have the following question about the exact transformation of the metric.


Suppose I have Vij=[xi1j1xi1j2xi2j1xi2j2]=[sin(t)cos(t)cos(w)sin(wt)] where ei={i,j}(cartesian coordinates x,y) and ej={r,θ}(polar coordinates)


In example, how to calculate the transformation gαi and gβk of Vαβ where eβ={i,j}(cartesian coordinates x,y) and eα={r,θ}(polar coordinates)?



Question 2, Suppose I had a variable(i.e. time or position) dependent unites, i.e. ei={(exp(t)+2,0),(0,exp(w)+2)}(vector pair was written in Cartesian coordinates) and ej={(t,0),(w,0)} how to calculate the exact expression of gij and gji and gij and gij? and what were they?



Answer



In general, it was not guaranteed that the transformation could be calculated out.


I.e. by redefine h=arcsin(t) and expand arcsin(t) to entire real axis by module. we could find dt/dsin(t). However it was not for sure that df(t)/dg(t,x) could always obtain a solution. Therefore the bases transformation of arbitrary functions in general could only be solve case by case.


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