Get error message for using Sx2

Question

I'd like to calculate Sx^2 in spin 1 system and the operator "Sx2" is defined in the spinone.h file. For the simplest example below, the compile was successful. But when I run the code, I got error message: "From line 161, file itdata/qdense.cc
Setting IQTensor element non-zero would violate its symmetry.
Setting IQTensor element non-zero would violate its symmetry."

include "itensor/all.h"

using namespace itensor;

int main()
{
auto sites = SpinOne(4);
ITensor op = sites.op("Sx2",2);
PrintData(op);
return 0;
}

I tried to modify the "opname" of "Sx2" and the content of "Sx2" in the spinone.h file, but still got the same error message. Unlike the case when I modify the the "opname" or content of "Sz", I got what I modified.

Other operators have the same problem: Sy2, XUp, XZ0, XDn.

Answer 1

Hi, thanks very much for pointing this out. It was a bug related to the implementation of the SpinOne site set within our new tensor storage system & site set design, which requires using a special temporary storage type for operators like this which don't respect the default symmetries associated with a site set. I just pushed a patch that ought to fix it for you.

It's a technical and confusing issue, although it doesn't cause any real problems when handled properly. But in a future version of ITensor I plan to eliminate the need for this workaround.

Miles