Hey, Can anyone help me to understand einstein notation and permutations? I have a book, but it's not very clear. I really don't understand how you can write A_ij = e_ijk a_k out as a matrix? To start with I understand that a matrix can be represented as A_ij where i is the row and j is the column. However, I don't understand as soon as k and the kronecker delta become involved! Anyone know of any good way to explain this or books or websites?? Thank you!!