Prevent duplicate connectors in Hamiltonian

Created by: femtobit

Continuing the discussion from #27:

But it is also because FindConn is not supposed to return duplicate terms (this is also checked for in one of the unit tests).

If I am not mistaken, the test you refer to currently checks for a different kind of duplication, namely, for duplicate target quantum numbers within each connector. Whether the connectors vector has duplicate entries, i.e., there exist k != j such that connectors[k] == connectors[j], is not checked. That case happens for the 2x2 PBC cube example, as there e.g. site (0,0) has two connectors to (0,1) (one "direct" and one "through the boundary").

This pull request adds a check for this scenario and disallows periodic boundaries for L<=2 hypercubes to prevent duplicate connectors there.

The case of merging local operators in CustomHamiltonian is still open for now.

requested review from @filippo.vicentini

Created by: gcarleo

Thanks @femtobit. Basically what you are doing here is to check that the Graph does not have duplicate Edges, if I understand correctly. I should know better, but is a similar check already done in CustomGraph ? If not, it would be great to add that check to complete this PR!

Created by: gcarleo

Actually the check is already performed here for CustomGraph https://github.com/netket/netket/blob/56ce86c886701867d2103ab290b5d68b0d18aed3/NetKet/Graph/custom_graph.hpp#L150

This check would fail if duplicate edges exist

Created by: gcarleo

Review: Approved

Looks good, useful to avoid issues with duplicate edges

Merged by: gcarleo at 2018-05-30 19:43:42 UTC

closed

mentioned in issue #248 (closed)