variational/indicial notation question

inprincipio

Dear All,

Not sure I'm posting in the correct subforum here, but I'm wondering if anyone can help me understand how to expand the following:

δu_i,j(δ_im+u_i,m)

I can't quite get to grips with the indicial notation in the example, the δu_i,j is the variation of u (displacement in this example) and the δ_im is the kronecker delta.. I just want to expand the brackets, can anyone offer any advice on how to do this.

Many thanks