Hi all, Firstly, I am not sure whether this is the area of the forum to ask this. I have been learning and researching a completely different topic, and from this I have come across a completely new concept of the Kronecker function. I have done a google search on this to get the intro and general background of how this function works. However, there is a particular problem which I cannot put my seem to get my head around. I have included the relevant equations below. I understand these equations EXCEPT for the Kronecker terms. From my understanding, the Cijkl equation can be expanded to obtain the C and C^p matrices. I do not fully understand how this process works, because I do not understand how to utilise the Kronecker function. In this context, I am guessing the i and j in the Kronecker terms represent the entry of the matrix, i.e if i=2, j=1, that means you are looking at the 2nd row and 1st column. And hence, you can go from there to calculate the term that goes into the particular matrix entry. What I do not understand are the "m" and "n" terms. What are they? What purpose do they serve? Can I just set any number for "m" and "n" Thanks in advanced for the help.