About Nabla and index notation

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SUMMARY

The discussion centers on the use of Nabla in index notation, specifically whether it can be treated as a vector when calculating curl, divergence, or gradient. The notation $$\nabla \times \vec{V} = \partial_i \hat{e}_i \times V_j \hat{e}_j$$ is identified as an 'abuse of notation' that can serve as a mnemonic but is not strictly correct. It is emphasized that while Nabla represents a covector (or dual vector), understanding its nuances is not essential for beginners. The conversation highlights the importance of bridging vector calculus with physical concepts while acknowledging the complexities of notation.

PREREQUISITES
  • Understanding of vector calculus concepts such as curl, divergence, and gradient.
  • Familiarity with index notation and its applications in physics.
  • Basic knowledge of covectors and their distinction from vectors.
  • Experience with mathematical notation and its implications in physics.
NEXT STEPS
  • Study the properties and applications of covectors in vector calculus.
  • Learn about the physical interpretations of curl, divergence, and gradient in fluid dynamics.
  • Explore advanced index notation techniques and their usage in tensor calculus.
  • Review vector identities and their proofs to solidify understanding of vector calculus.
USEFUL FOR

This discussion is beneficial for students of physics and mathematics, particularly those studying vector calculus and its applications in physical theories. It is also useful for anyone looking to clarify the relationship between mathematical notation and physical concepts.

Remixex
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Homework Statement


Can I, for all purposes, say that Nabla, on index notation, is $$\partial_i e_i$$ and treat it like a vector when calculating curl, divergence or gradient?
For example, saying that $$\nabla \times \vec{V} = \partial_i \hat{e}_i \times V_j \hat{e}_j = \partial_i V_j (\hat{e}_i \times \hat{e}_j) = \partial_i V_j \epsilon_{ijk} \hat{e}_k$$
I have a feeling that is wrong, I've found all kinds of variations of this notation on the internet, almost no one seems to use the unit vectors, and that confuses me, being a total beginner on this kind of notation.

Homework Equations


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The Attempt at a Solution


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It's an 'abuse of notation', but it can be useful as a mnemonic. If it helps you remember the formulas, that's fine. But try not to lose sight of the fact that it is not strictly correct. For instance ##\nabla f## is not strictly a vector (it's a covector, aka one-form or dual vector). You probably don't need to understand nuances like that yet if you're just starting but it's good to remember that the notation is just a mnemonic, to avoid confusion later on.
 
Yes i have very clear what do gradients or divergences do...in a practical way (direction of max change, and flux per EDIT:volume unit :) i believe?) but I'm still struggling setting up the bridge between my vector calculus knowledge, physics knowledge, and this notation... But the course is only starting, and I'm trying to prove vector identities.

Thanks for the response :)
 

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