Reduced density matrix of nonadjacent sites

[vyason]

Hi @adityab999

Yes. the original is posted here:

Is this a correct way to calculate one-site and two-site entanglement spectrum and entropy?

Hello everyone! Here I want to calculate the one-site and two-site entropy to obtain the mutual information. With the guides of these disccusion 1-RDM from Julia version - ITensor Julia Questions - ITensor Discourse, Mutual Information matrix - DMRG and Numerical Methods - ITensor Discourse and Two-site reduced density matrix - ITensor Julia Questions - ITensor Discourse, I wrote some test codes to ahieve my goal. But nearly all of the returned eigenvalues are zero, except for one value that …

I also tried a lot for extending it to 3-site RDM. However:

1. The final tensor only has the indices the indices of the sites on the very left and the very right, but not for the intermediate one.
2. There are alwyas leftover links in the resulting tensor object.

Hope somebody will figure it out.

A