# Another index notation question hopefully pretty easy

How do I make sense of the index notation expression

$$r_j r_i p_j$$

?

What I really *want* it to be is

$$\vec{r} (\vec{r} \cdot \vec{p})$$

And it turns into this, as long as I can commute the $r_i[/tex] and [itex]r_j$...right?

(By the way, here $\vec{r}$ is just the position vector and $\vec{p}$ is the momentum vector.)

HallsofIvy