- #1

Sophia Clark

- 2

- 0

## Homework Statement

Hi all!

I'm having trouble understanding the implementation of some derivatives in the expression (1) of this article:

https://www.ncbi.nlm.nih.gov/pubmed/26248210

How do I implement ∑

_{(ij)}∂

_{ij}w ?

Thank you all in advance.

## Homework Equations

w is a square matrix(120x120) with periodic boundary conditions.

## The Attempt at a Solution

I understood it as the second derivative of the matrix w, but it doesn't seem to be correct.