- #1

- 533

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Let [itex]\vec{x}[/itex] be the position vector and [itex]\vec{r}[/itex] the radial unit vector. In index notation, I find myself confronted with simplifying

[tex]

x_k \partial_i r_k.

[/tex]

I desperately want this to be zero, but I can't figure out why it should be. (I can't really figure out what this represents at all, as a matter of fact.) Isn't [itex]\partial_i r_k[/itex] a 2 by 2 matrix? And if so, how would multiplying with [itex]x_k[/itex] make everything go away? Again, maybe it doesn't.

Can anyone help?