Product of a third- and second-order tensor.

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Discussion Overview

The discussion revolves around the multiplication of a third-order tensor with a second-order tensor to yield a vector, specifically in the context of the relationship between the polarization vector and the stress tensor in piezoelectric materials. The conversation explores the mathematical operations involved, including tensor contraction and component extraction.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents the equation \(\vec{P}=\underline{\underline{d}} \: \underline{T}\) and seeks clarification on the multiplication process of the tensors.
  • Another participant suggests that the operation may involve contraction, proposing a formula for obtaining the components of the resulting vector.
  • A participant describes the process of extracting the "i-th" component of the vector by taking an "i-th slice" of the third-order tensor and multiplying it with the second-order tensor, emphasizing that this is not standard matrix multiplication.
  • There is a clarification that contracting over two indices results in a sum of products of the tensor components, leading to a component of the vector.
  • One participant confirms the understanding of the contraction process as involving the summation of nine products from the tensor components.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the tensor multiplication process, with some agreeing on the contraction method while others seek further clarification. The discussion does not reach a consensus on the best approach or interpretation of the tensor operations.

Contextual Notes

Some participants note the complexity of the tensor operations and the potential for confusion regarding the definitions and methods of multiplication. There is also a mention of a lack of references, which may limit the clarity of the discussion.

Who May Find This Useful

This discussion may be useful for students or researchers interested in tensor mathematics, particularly in the context of piezoelectric materials and their properties.

Nimlidor
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Hi,
I have read that vector of polarisation [itex]\vec{P}[/itex] and stress tensor T are linked with equation
[itex]\vec{P}=\underline{\underline{d}} \: \underline{T}[/itex]
where d is a third-order piezoelectric tensor. Can anyone explain how you multiply a third and a second-order tensor to get a vector? A good link will also help.
Thank you,
N.
 
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I'm not familiar with this equation, but I'm guessing that it's a contraction: ##A_{i}=\sum_{j,k}B_{ijk}C_{jk}##.

Also, it's usually a good idea to include a better reference than "I have read...". It might be easier to answer if we knew where you read it. If possible, you should link directly to the relevant page at Google Books.
 
So if I understand this correctly, in order to get "i-th" component of a vector you have to take i-th "slice" of third-order tensor and multiply it with second order tensor: not in the standard way we multiply matrices, but rather just multiply j,k-th component of both tensors and sum over all nine components (assuming that both tensors are three dimensional)?
I would have included a reference, but I only have it in printed version in Slovenian. :blushing:
 
Nimlidor said:
So if I understand this correctly, in order to get "i-th" component of a vector you have to take i-th "slice" of third-order tensor and multiply it with second order tensor: not in the standard way we multiply matrices, but rather just multiply j,k-th component of both tensors and sum over all nine components (assuming that both tensors are three dimensional)?
You certainly don't have to do this to obtain the ith component of an arbitrary vector. What I'm saying is if you take a tensor with 3 indices and one with 2, and "contract" two indices as I did, the result is a component of a vector.
 
Does contracting over two indices mean that you make a sum of nine products?
[itex]B_{i11}C_{11}+B_{i12}C_{12}+B_{i13}C_{13}+...+B_{i32}C_{32}+B_{i33}C_{33}[/itex]
 
Yes, that's what it means.
 
Thank you very much!
 

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