A potential low level bug with MPS class

Question

Hello,

I find the following issues with MPS class, which I assume are hidden bugs(certainly, fault could be mine). Generally, under some circumstances, the memory allocated to the program exceeds severely it's supposed to need and the whole program seems to fail to terminate peoperly. By saying "some circumstances" I refer to:

when a MPS object is modified by functions(for example, readFromFile) to which the MPS object is passed by reference and functions, which involve matrix multiplication such as overlap and exactApplyMPO, are applied to it.

Specifically, the system I'm working on is a toy-like 4*4 lattice with nearest neighbor Heisenberg Model. It's observed via htop that over 10GB memory is allocated for such calculation, while when such calculation is carried out properly it only requires a few hundreds MB and less than a second.

The way I work this around is to define and modify all MPS inside the main function, which will not be a good idea as the project grows larger. I eagerly look for help and present my thank in advance.

Comments

Just to follow up on what the resolution of the issue was (for readers of this thread). The exactApplyMPO function was allowing the user to pass an MPS and an MPO which had different site indices, causing the bug to happen. The fix is to make sure that the MPS and MPO have the same site indices, but I am also putting a check into exactApplyMPO to give a useful error message in the future.

Answer 1

Hi, thanks for the report - could you please email me a code that reproduces the issue? (Ideally with the minimal amount of code and running time to still see the issue.) Otherwise I don't know if I'll be able to see where it could be happening since I haven't been observing this behavior.

Thanks!

Miles

Comments

Hi Miles,

I've sent to your flatiron email a succinct code example that exhibits the bug.

Thanks!