MPS simulator with low limits can crash #2290
Description
Informations
- Qiskit Aer version: Latest development version.
- Python version: Doesn't matter, the issue was noticed by using qiskit aer from c++
- Operating system: Windows 11, but it's probably present on all available
What is the current behavior?
It's not a big issue, as it's avoidable, but anyway, I thought I should report it.
Setting a big value for the singular values threshold can crash the MPS simulator.
Steps to reproduce the problem
I caught this accidentally by generating and executing random circuits (over 100 gates) on a MPS simulator with 50 qubits, with drastic limits set (something like 15 for max bond dimension and 0.05 for truncation threshold), so it's probably not very easy to reproduce...
A crash that I managed to reproduce happened in csvd, more precisely on this line:
k had a big value, something like 210310 while size was 4.
A had 4 rows and 0 columns for this case, my guess is that due of the big truncation value somehow along the way one of the dimensions gets 0 and that is the source of the issues.
The problem seems to be generated by the too big truncation threshold, if I set it to a lower value, I cannot reproduce the issue anymore.
What is the expected behavior?
Not crashing, obviously.
Suggested solutions
Probably matrices shouldn't be truncated down to 0 dimension(s), if 0 is obtained it should be changed to 1 or something like that, but this is a wild guess.