Lanczos_Gnd -> Tridiag error

[chiamin]

When doing DMRG, from time to time the program is stopped and I got the following message:

[WARNING] Lanczos_Gnd -> Tridiag error: 

Lanczos continues automatically.

# Cytnx warning occur at void cytnx::linalg::_Lanczos_Gnd_general_Ut(std::vector<cytnx::UniTensor>&, cytnx::LinOp*, const cytnx::UniTensor&, const bool&, const double&, const unsigned int&, const bool&)
# warning: [WARNING] iteration not converge after Maxiter!.
 :: Note :: ignore if this is intended

Is it due to the non-convergence of Lanczos? If this is the case, I have the following suggestions.

1. Make it a warning rather than an error.
2. If this is indeed an error and if we want it to be an error, show it as an error in the error message.

I didn't dig into the code so do not really know why it stopped though...

[j9263178]

I think it has nothing to do with the non-convergence warning, there's an error in the tridiag and it is not printed out.