Understanding the Colon Notation:

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Discussion Overview

The discussion revolves around the meaning and implications of the colon notation, :, particularly in the context of integrals and weak solutions in mathematics. Participants explore its application in various mathematical constructs, including inner products and dyadics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants inquire about the general meaning of the colon notation, :, in mathematical contexts.
  • There is a specific question regarding the meaning of the colon notation when used inside an integral for weak solutions.
  • One participant suggests that $$\mathbf{x}\otimes\mathbf{x}:y$$ may be equivalent to $$\langle\mathbf{x}\otimes\mathbf{x}, y\rangle$$, which denotes an inner product, but expresses uncertainty about the elementary nature of the question.
  • Another participant questions what is being multiplied in the expressions involving the colon notation.
  • There is a mention of locally integrable functions represented as $$\mathbf{x}=(x_1({\cdot}), x_2({\cdot}), x_3(\cdot))$$ and how this relates to constructing a rank one $$3\times 3$$ matrix for multiplication with $$y$$.
  • One participant raises the connection between the colon notation and distributions, seeking clarity on the relationship.
  • A later reply notes that the colon can signify a double dot product, referencing external sources, but emphasizes the ambiguity surrounding the variable $$y$$.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the colon notation and its application, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

The discussion highlights ambiguities in definitions and the context of the notation, particularly regarding the nature of the variables involved and the operations being performed.

Integrals
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What does the colon notation, :, mean?
 
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Integrals said:
What does the colon notation, :, mean when it is inside an integral for weak solutions?
Can you be a bit more precise and descriptive?
 
fresh_42 said:
Can you be a bit more precise and descriptive?
Apologies for the confusion, is it correct to say that $$\mathbf{x}\otimes\mathbf{x}:y$$ is equivalent notation for $$\langle\mathbf{x}\otimes\mathbf{x}, y\rangle$$ where the latter denotes the inner product. Perhaps, this question was more elementary than I had meant...
 
I haven't seen the first one, and the second one calls for the question, what are you multiplying there?
 
fresh_42 said:
I haven't seen the first one, and the second one calls for the question, what are you multiplying there?
Locally integrable functions - where $$\mathbf{x}=(x_1({\cdot}), x_2({\cdot}), x_3(\cdot))$$
 
How is this related to distributions?
 
Integrals said:
Locally integrable functions - where $$\mathbf{x}=(x_1({\cdot}), x_2({\cdot}), x_3(\cdot))$$
If I build the ##\mathbf{x} \otimes \mathbf{x}## from this, I get a rank one ##3\times 3## matrix. How can this be multiplied by an ##y## via an inner product, wherever this is from?
 
The colon can signify a double dot product (see the wikipedia page on Dyadics). It is still ambiguous what is going on here. What is ##y##?
 

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