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Tensor Inverse?
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Hauke Reddmann
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Joined: 03 May 2005
Posts: 112

PostPosted: Wed Jun 28, 2006 8:16 am    Post subject: Tensor Inverse? Reply with quote

Is there something that could be termed "inverse" to
a tensor like, say, T^i_jk? If the "determinant" is
nonzero? And even more, if yes, does T*U=T*V imply
U=V?

--
Hauke Reddmann <:-EX8 fc3a501@uni-hamburg.de
His-Ala-Sec-Lys-Glu Arg-Glu-Asp-Asp-Met-Ala-Asn-Asn
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Robert Low
science forum Guru


Joined: 01 May 2005
Posts: 1063

PostPosted: Wed Jun 28, 2006 8:41 am    Post subject: Re: Tensor Inverse? Reply with quote

Hauke Reddmann wrote:
Quote:
Is there something that could be termed "inverse" to
a tensor like, say, T^i_jk? If the "determinant" is
nonzero? And even more, if yes, does T*U=T*V imply
U=V?

You can think of a tensor as a linear operator
(generally in many different ways). No reason
why some of them shouldn't have inverses.

For example, you might have some vector space
V, and T is in V \otimes V \otimes V* \otimes V*
(where \otimes means tensor product). Then you
can think of T as a linear map from V* \otimes V*
to V* \otimes V*, or as a linear map from
V \otimes V* to V \otimes V*, or from V to
V \otimes V \otimes V*, or ....

Then you can pick bases for the domain and codomain
of the tensor thought of as a linear mapping with that
domain and codomain, express your tensor with respect
to those bases, and do what you'd normally do with
the resulting matrix.
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Timothy Murphy
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Joined: 29 Apr 2005
Posts: 275

PostPosted: Thu Jun 29, 2006 2:29 pm    Post subject: Re: Tensor Inverse? Reply with quote

Hauke Reddmann wrote:

Quote:
Is there something that could be termed "inverse" to
a tensor like, say, T^i_jk? If the "determinant" is
nonzero? And even more, if yes, does T*U=T*V imply
U=V?

It isn't clear what you mean by T*U .

--
Timothy Murphy
e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland
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Hauke Reddmann
science forum Guru Wannabe


Joined: 03 May 2005
Posts: 112

PostPosted: Fri Jun 30, 2006 9:32 am    Post subject: Re: Tensor Inverse? Reply with quote

Timothy Murphy <tim@birdsnest.maths.tcd.ie> wrote:
Quote:
Hauke Reddmann wrote:

Is there something that could be termed "inverse" to
a tensor like, say, T^i_jk? If the "determinant" is
nonzero? And even more, if yes, does T*U=T*V imply
U=V?

It isn't clear what you mean by T*U .

U and V are tensors, T*U is standard multiplication in
index form (and that may even contain some implicit
Einstein summation - could be relevant)
--
Hauke Reddmann <:-EX8 fc3a501@uni-hamburg.de
His-Ala-Sec-Lys-Glu Arg-Glu-Asp-Asp-Met-Ala-Asn-Asn
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Timothy Murphy
science forum Guru Wannabe


Joined: 29 Apr 2005
Posts: 275

PostPosted: Fri Jun 30, 2006 11:37 am    Post subject: Re: Tensor Inverse? Reply with quote

Hauke Reddmann wrote:

Quote:
Timothy Murphy <tim@birdsnest.maths.tcd.ie> wrote:
Hauke Reddmann wrote:

Is there something that could be termed "inverse" to
a tensor like, say, T^i_jk? If the "determinant" is
nonzero? And even more, if yes, does T*U=T*V imply
U=V?

It isn't clear what you mean by T*U .

U and V are tensors, T*U is standard multiplication in
index form (and that may even contain some implicit
Einstein summation - could be relevant)

That still doesn't clarify it, at least for me.
What exactly are U,V?

Incidentally, the tensor T^i_jk has a unique
Penrose/Moore generalized inverse X_i^jk ,
at least of you are working over the complex numbers.

--
Timothy Murphy
e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland
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