Defining the Tensor Product of Gradients for Different Coordinate Systems

In summary, the conversation discusses the definition of ##\nabla \otimes \nabla f## and its relationship to the coordinate system. While its components may vary in different coordinates, the tensor itself does not change. The conversation also mentions the gradient of a vector and the presence of Christoffel symbols. It is suggested to refer to equations for the gradient in a specific coordinate system for more information.
  • #1
member 428835
Does anyone know where I can find the definition of ##\nabla \otimes \nabla f##? I tried googling this but nothing comes up. I know it will change depending on the coordinate system, so does anyone know the general definition OR a table for rectangular, spherical, cylindrical coordinates?

Thanks so much.
 
Physics news on Phys.org
  • #2
It does not change with the coordinate system. That is the entire point. However, its components in a particular coordinate system may be different.

It is the tensor you obtain by taking the gradient twice.
 
  • #3
Orodruin said:
It does not change with the coordinate system. That is the entire point. However, its components in a particular coordinate system may be different.

It is the tensor you obtain by taking the gradient twice.
Okay, so in cylindrical coordinates, for example, ##\nabla f = \langle f_r , f_\theta r^{-1}, f_z\rangle##. So does this imply $$\nabla \otimes \nabla f =
\begin{bmatrix}
f_r^2 & f_r f_\theta r^{-1} & f_r f_z\\
f_\theta r^{-1} f_r & f_\theta^2 r^{-2} & f_\theta r^{-1} f_z\\
f_rf_z & f_z f_\theta r^{-1} & f_z^2
\end{bmatrix}$$
 
  • #4
No, you are missing all of the terms involving Christoffel symbols that you get when taking the gradient of a vector
 
  • Like
Likes member 428835
  • #5
Ohhhhh yeaaaa, because the unit vectors change with position. Is there a table anywhere with this information? I'd prefer not to derive it all from scratch if I can help it.
 
  • #6
All you need to do is look up the equations for the gradient of a vector for your particular coordinate system, since ##\nabla f## is a vector.
 

1. What is the tensor product of gradients?

The tensor product of gradients is a mathematical operation that combines two gradients to create a new tensor. It is commonly used in machine learning and deep learning algorithms to calculate the gradient of a multi-variable function.

2. How is the tensor product of gradients calculated?

The tensor product of gradients is calculated by taking the outer product of the two gradients. This means multiplying each element of one gradient with each element of the other gradient, resulting in a new tensor with dimensions equal to the product of the dimensions of the original gradients.

3. What is the purpose of using the tensor product of gradients?

The tensor product of gradients allows for the calculation of the gradient of a multi-variable function, which is necessary for optimizing parameters in machine learning and deep learning algorithms. It also helps in understanding the relationship between different variables in a function.

4. Can the tensor product of gradients be applied to any type of function?

Yes, the tensor product of gradients can be applied to any type of function, as long as the function is differentiable. This means that the function must have a well-defined derivative at every point in its domain.

5. Are there any limitations to using the tensor product of gradients?

One limitation of using the tensor product of gradients is that it can be computationally expensive for high-dimensional functions. Additionally, it may not be suitable for non-linear functions or functions with complex relationships between variables.

Similar threads

  • Differential Geometry
Replies
2
Views
513
  • Differential Geometry
Replies
9
Views
411
Replies
16
Views
3K
  • Linear and Abstract Algebra
Replies
7
Views
238
  • Differential Geometry
Replies
7
Views
3K
Replies
10
Views
2K
  • Quantum Physics
Replies
4
Views
658
Replies
37
Views
8K
Replies
2
Views
2K
Replies
3
Views
2K
Back
Top