# Notation issue: Grad with a vector subscript

by Hoplite
Tags: grad, issue, notation, subscript, vector
 P: 40 I'm reading a journal article at the moment which uses a piece of notation which they dont actually define. It looks like this: $$\nabla_{\vec Q}$$ (As it happens, $$\vec Q$$ is an ordinary vector indicating the orientation of a polymer.) I've never seen vector subscript on the gradient symbol "$$\nabla$$" before. Could anyone please tell me what $$\nabla$$ with a vector subscript usually means?
 Math Emeritus Sci Advisor Thanks PF Gold P: 39,552 First, since you mention polymers, I am inclined to think the symbol has more to do with chemistry than mathematics. If it really is purely mathematics then I would be inclined to think "the derivative in the direction of $\vec{Q}$".