Notation issue: Grad with a vector subscript

Hoplite

I'm reading a journal article at the moment which uses a piece of notation which they dont actually define. It looks like this:

[tex]\nabla_{\vec Q}[/tex]

(As it happens, [tex]\vec Q[/tex] is an ordinary vector indicating the orientation of a polymer.)

I've never seen vector subscript on the gradient symbol "[tex]\nabla[/tex]" before.

Could anyone please tell me what [tex]\nabla[/tex] with a vector subscript usually means?

HallsofIvy

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 [itex]\vec{Q}[/itex]".

Hoplite

Thanks, the derivative in the direction of the vector makes sense in context.