Compatibility problem for reading MPS from disk

Question

Dear all,

I have encountered some problem when I tried to update my code for the v3 version. I have saved some IQMPO and IQMPS to disk before in the v2 version, but now I can not read those in the v3 version. Is there anyway that I could adjust the file or the code for this?

In addition, the prime(itensor, args) function doesn't seem to support combinations of Tags and Indexsets anymore in v3, where in v2 I could use prime(itensor, Tags, Index). Is it true or am I missing something?

Thanks.

Best,

Yixuan

Answer 1

Hi Yixuan,
To answer your first question, at the moment the file formats used by ITensor are not guaranteed to be stable to version changes, due to the fact that we write out the binary representation of objects in memory. So they are also not guaranteed to work across different machines with different binary formats. So it's still a useful feature for writing objects to disk and reading them back throughout a single calculation or within the same version of ITensor, but not meant as a long-term storage solution.

One feature we are planning to add after we first address some other things is to add support for HDF5. Then we can have long-term stability of ITensors written to disk.

To answer your other question, I think you are right that combining TagSets and Index's in the prime function doesn't currently work. So as a work-around for now, please just call prime twice with the different arguments you would like to use and that should work. But also could you please file an issue about allowing this combination since I think it would be straightforward for Matt to add it.

Thanks,
Miles

Comments

Miles,

Thank you very much for the clarification! I will file this issue.

Best,

Yixuan