# Homework Help: Gradient of vector

1. May 29, 2008

### enricfemi

$$\nabla$$$$\stackrel{\rightarrow}{A}$$

when a gradient operater act on a vector,what is it stand for ?

2. May 29, 2008

### D H

Staff Emeritus
Visually, what you wrote looks like

$$\nabla_{\vec A}$$

$$\nabla \vec A$$

These are two different things. The first is an operator, the gradient with respect to the components of $\vec A$, rather than the normal gradient which is take with respect to spatial components. The second form is the gradient of a vector. It is a second-order tensor. If $$\vec A = \sum_k a_k \hat x_k$$,

$$(\nabla \vec A)_{i,j} = \frac{\partial a_i}{\partial x_j}$$

BTW, it is best not to separate things the way you did in the original post. Here is your original equation as-is:

$$\nabla$$$$\stackrel{\rightarrow}{A}$$

Now look at how this appears when written as a single LaTeX equation:

$$\nabla\stackrel{\rightarrow}{A}$$

Last edited: May 29, 2008
3. Sep 22, 2009

### dakg

Does this make a matrix using row i and column j for the entries?

4. Sep 22, 2009

### D H

Staff Emeritus
Yes.

5. Sep 22, 2009

Thank you.