Random UserWarning: unused option ['P_tol']

How do I use this algorithm? What does that parameter do?
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Random UserWarning: unused option ['P_tol']

Post by xaver »

I frequently and randomly get the warning UserWarning: unused option ['P_tol'] for config lanczos_params warnings.warn(msg.format(keys=sorted(unused), name=self.name)) when starting a dmrg run.

I get this warning independent of if I do, or if I do not use 'lanczos_params': {'P_tol': some integer,} in the dmrg_params.

And, strangely enough, if it is not a batch-run, and I see the warning to occur, and then stop and restart the dmrg run 'by hand', the warning frequently does not show up again.

Is this expected behavior, should I worry about it / dismiss it, can I stop it?
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Re: Random UserWarning: unused option ['P_tol']

Post by Johannes »

By default, the option `P_tol_to_trunc` causes DMRG to set the P_tol parameter in the lanczos_params, which causes this warning in case DMRG actually does not use lanczos to diagonalize the effective Hamiltonian (it does exact diagonalizaiton for small enough chi where this is actually faster).

I've updated this in 5fcdea9181e5a4ebdc8c0aaa77572aa40ab708eb such that it should no longer print a warning; please let me know if it still does.
Thanks for pointing it out!
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