Evaluating Expressions with Kronecker Delta

[Hendrick]

Homework Statement

Simplify/Evaluate these expressions involving the Kronecker delta, using Einstein's summation convention:
a)\delta_{qr}\delta_{rp}\delta_{pq}
b)\delta_{pp}\delta_{qr}\delta_{rq}

Homework Equations

\delta_{ij}=0 when i =/= j
\delta_{ij}=1 when i = j

The Attempt at a Solution

a)\delta_{qr}\delta_{rp}\delta_{pq}
=\delta_{qp}\delta_{pq}
=\delta_{qq} = 3 (summation over repeated q)

b)\delta_{pp}\delta_{qr}\delta_{rq}
=\delta_{pp}\delta_{qq}
=(3)(3)
=9
[Am I actually able to evaluate the \delta_{qr}\delta_{rq} part before the \delta_{pp} part, I mean you can't do that with matrices... :S]


Thank you

 

[phyzguy]

I think what you did is correct. If you think of them as matrices, remember they are identity matrices, so they commute with everything, so the order does not matter.