Question about fix_qeq_point.cpp

I have a question about the fix_qeq_point.cpp. When we create the H matrix, why don’t we also include the elements in the matrix for those tag[i] > tag[j]?

Here is the codes I am talking about. I think it is related to how the matrix is stored, but I am not quite sure.

I have a question about the fix_qeq_point.cpp. When we create the H matrix,
why don't we also include the elements in the matrix for those tag[i] >
tag[j]?

r_ij is equal to r_ji and thus the matrix will be symmetric, so why do
double the work?

That’s right. Then the problem I don’t understand is in this fix a full neighbor list is used. If j < n, I think it is possible for these local pairs has the property tag[i] > tag[j].

Yi

The code for the neighbor list