Definition of the Lagrangian finite strain tensor

[albus]

The Lagrangian finite strain tensor is defined as:

$$E_{i,j}=\frac{1}{2}\left(\frac{\partial x_k}{\partial X_i}\frac{\partial x_k}{\partial X_j}-\delta _{i,j}\right)$$

Is it in Einstein Notation so that there is a summation symbol missing, i.e. would it be the same thing if one wrote it as:

$$E_{i,j}=\frac{1}{2}\left(\sum _k \left(\frac{\partial x_k}{\partial X_i}\frac{\partial x_k}{\partial X_j}\right)-\delta _{i,j}\right)$$

It's that there is too many indices in mechanics, and it always gets me confused. Thanks a lot!

 

[Chestermiller]

Yes. this would involve use of the Einstein summation convention.