# Error: "Default constructed ITensor in product"

+1 vote
asked Aug 14

While attempting to import a wavefunction and site data from files, and then analyze the wavefunctions, I got the following error:

From line 101, file itensor_operators.cc

Default constructed ITensor in product


Is this error message consistent with some kind of error in the wavefunction file that is somehow jamming either the import or analysis of the wavefunction?

## 1 Answer

+1 vote
answered Aug 14 by (19,400 points)

Hi Jon,
Yes I somtimes get that message when a file is made using a previous version of ITensor. We try to keep backwards compatibility of the file formats but currently the only guarantee is that files read using the same version of ITensor, on the same computer, are guaranteed to work correctly. ("Guaranteed" means what we consider a bug or not.)

So is it possible you wrote the file with a previous version of ITensor? If so that could be the culprit.

If not, can you tell me how you created the file? Like did you make it on a different computer possibly?

Miles

commented Aug 15 by (500 points)
I am running ITensor on COMET at the SDSC and I didn't allocate enough RAM for the calculation that produced the wavefunction and sites files. I am not sure, but I suspect that when I then imported these files for a subsequent calculation, they were incomplete. I did not get this error when the memory allocation was sufficient.

I asked the question to make sure that I am not misinterpreting the error.
commented Aug 15 by (19,400 points)
Hi Jon, yes if a file is not successfully written then I think that is very likely the cause of this error. It's a cryptic error I agree, but we haven't put in facilities for writing tensors to disk in a "transactional" way yet, meaning that either a whole tensor gets written or not at all. The reason is mainly that we are trying to keep the number of dependencies ITensor has very low, since other libraries are often surprisingly quite hard to install. I think in the future I will start providing optional dependencies, where people can turn on fancier features if they have certain libraries on their system (such as HDF5 for writing structured data files).
commented Aug 16 by (500 points)
Ok thanks.  I think the file did get written, since my program spent 30 minutes processing the imported wavefunction before the error came up.
commented Aug 16 by (500 points)
In the case where the file was empty, it came back with an error in a matter of seconds.