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The scalar no scalar mystery
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Short working note dated 11.22.15 comparing two treatments of a rank-1 tensor function. It sets the Chapter 2 scalar-field rule α(v)=α'(v') against the Appendix D rule α'(v)=α(v'), and resolves the mystery as a difference between component transformations and vector transformations. It then checks the rank-2 case, showing T'(v'1,v'2)=T(v1,v2) using R orthogonality.
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The scalar no scalar mystery. 11.22.15
Here is the discussion on this subject ,
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Scalar under transformations
Imagine a version of Picture A (2.1.1) where we transform from x-space with basis vectors ei to some x'-space with basis vectors e'i. Under such a transformation, a dot product like α v transforms as a scalar. So, whereas v and α transform as vectors, the function α(v) transforms as a scalar field, just as in (2.2.6). That is to say,
α(v) = α v = α' v' = α'(v') . (2.11.13)
Although the function α(v) transforms as a scalar, the associated vector α (covector) transforms as a rank-1 tensor (vector), and it is through this isomorphic connection that we loosely refer to the function α(v) as being a rank-1 tensor. When functional α is expanded on the basis functionals λi, the coefficients αi are the rank-1 tensor components, and these coefficients are projected out by (2.11.9).
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In App D tensor functions are somehow not scalars. What does App D say about a vector functional?
<T | vi> = T(vi)
Ti = T(ei) MIJ = (vj)i
T(vi) = Σj (vi)j Tj
α(vi) = Σj (vi)j αj
α(vi) = Σj (vi)j αj αj = corresponding rank-1 tensor (vector)
= vi α // there it is, finally; sure looks like a "scalar".
α(v) = Σj vj αj αj = corresponding rank-1 tensor (vector)
= v α // there it is, finally; sure looks like a "scalar".
Jump ahead to my transformation rule applied to a rank-1 tensor function.
α'(v1) = α( R1jvj) = α(v'1) = R1jα(vj) v1 = R1beb
Well the equation can be selected to be
α(v'i) = Rijα(vj) = α'(vi) v'i = Rij vj α'
Where is "scalar" now? App D says this is the transformation rule for a rank-1 tensor function.
HERE, Rij are the lincom transformation coefficients which generate v'i from vi . THAT is the underlying transformation being talked about in my App D interpretation.
Side by side:
α(vi) = α vi = α' vi' = α'(vi') v'i = Rij vj Chapter 2
α'(vi) = α(v'i) = Rijα(vj) v'i = Rij vj Appendix D
Comment: The first line uses some component transformation
(v'i)a = Rab (vi)b
(α'i)a = Rab (αi)b
and the second line use a vector transformation, so that explains the mystery.
What happens at the k = 2 level?
T(v'i,v'i) = RijRijT(vj,vj)
T(v1,v2) = Σab Tab (v1)a(v2)b
Under a coordinate transformation you would say
T'(v'1,v'2) = Σab Tab (v1')a(v2')b
(v1')a = Rar(v1)r
(v2')b = Rbs(v2)s
T'ab = RadRbeTde // these three lines are all component transformations
Then
T'(v'1,v'2) = Σab T'ab (v1')a(v2')b
= RadRbeTde Rar(v1)r Rbs // all implied sums
= RadRbeRarRbs (v1)r(v2)s
= (RadRar)(RbeRbs) Tde(v1)r(v2)s
= δdrδesTde(v1)r(v2)s
=Tde(v1)d(v2)e
=Tab(v1)a(v2)b
= T(v1,v2)
=
= RabRbc Σab Tab(v1)b (v2)c
D.4 Two kinds of transformations