About Nabla and index notation

In summary, the conversation is discussing the use of Nabla and its index notation as a vector when calculating curl, divergence, and gradient. It is mentioned that this notation is an 'abuse of notation' and not entirely correct, but can be useful as a mnemonic. The conversation also touches on the notation being a bridge between vector calculus and physics knowledge.
  • #1
Remixex
57
4

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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  • #2
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.
 
  • #3
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 :)
 

1. What is Nabla in index notation?

Nabla, also denoted as ∇, is a mathematical operator used in vector calculus to represent the gradient of a scalar field or the divergence of a vector field. In index notation, it is represented as ∇ = (∂/∂x, ∂/∂y, ∂/∂z).

2. What is index notation?

Index notation is a mathematical notation used to represent vectors, tensors, and other mathematical objects using indices instead of coordinates. It is commonly used in vector calculus and tensor analysis to simplify and generalize mathematical expressions.

3. How is Nabla used in index notation?

In index notation, Nabla is used to represent the gradient of a scalar field (∇φ) or the divergence of a vector field (∇·A). It can also be used to represent the Laplacian operator (∇²).

4. What are the advantages of using index notation?

Index notation allows for a more compact and concise representation of mathematical expressions. It also enables easier manipulation of equations and simplifies the notation for complicated vector and tensor operations.

5. Can index notation be used in other fields of science?

Yes, index notation is not limited to mathematics and can be used in other fields of science, such as physics and engineering. It is particularly useful in fields that deal with vector and tensor quantities, such as electromagnetism and fluid mechanics.

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