TeNPy Forum

Hi!

In MPS.expectation_value, use the axes parameter.
Hope this already helps, if not, post again =)

Cheers
Jakob

Have a look at the models guide

https://tenpy.readthedocs.io/en/latest/intro/model.html

If you need a finite periodic system, simply dont inherit from NearestNeighbourModel, then you can still do everything except TEBD

This is expected behavior.
The nearest neighbor model needs to be nearest neighbor in the MPS geometry of an open chain. From the MPS point of view, your model has one single long range coupling between the first and last site.
You can have such a model with infinite MPS, but not with finite MPS

See https://github.com/tenpy/tenpy/pull/529

See https://github.com/tenpy/tenpy/pull/529

Hi, Based on a quick look at https://tenpy.readthedocs.io/en/latest/reference/tenpy.simulations.time_evolution.TimeDependentCorrelation.html#tenpy.simulations.time_evolution.TimeDependentCorrelation I assume that a list as operator_t0 has a different meaning, it will apply them all instead of loopin...

Hi,

GPUs are not supported yet. We are working on it for version 2. We hope to get a working pre-release version ready before christmas.

Hi, the AKLTChain is one of the few models in tenpy that is not defined via the CouplingModel framework, so this error is expected behavior. If you want to modify the existing AKLTChain, take a look at how it is defined and adjust the ``H_bond`` in ``__init__`` to include your extra term. Note that ...

Also note that for an Sz conserving state, <Sp Sp> = 0 = <Sm Sm>.

It is not possible to have an Sx operator when conserving Sz, precisely because applying Sx has no well defined action on the conserved Sz charge. You can think of the action of Sx as a superposition of both raising and lowering the Sz charge. This can not be done while enforcing Sz conservation. Yo...

Hi,
This looks correct, and seems like a good implementation of your goal.
I am not sure why you would want to do this random truncation in the first place, but the code should be able to do it nicely.

Hi, These types of position dependent charges are not available in the live tenpy version yet There is an unmerged PR at https://github.com/tenpy/tenpy/pull/183 It seems, however, that it is not very stable for infinite systems and not tested well enough. I would not blindly trust it. In the infinit...

The code you pasted already fails before this line. E.g. Sx = [model.lat.mps_sites().Sx for i in range(L)] fails, as model.lat.mps_sites() is a list. The failure you report is expected behavior as well. An operator, like the entries in your Sx list are Arrays and do not know what site they came from...

1) - line before the three: initialize a BosonSite, with its opertors etc. next we modify it by adding the new operator - extract alpha from the model_params, this is just a convenient way to tell the model the value for alpha - N_diag is a helper for defining the operator. It is the diagonal of the...

The operator you want is not one of the pre-defined operators of the BosonSite, so you would need to add it explicitly. You probably want to do something like this: class MyExtendedBoseHubbarModel(tenpy.BoseHubbardModel): def init_sites(self, model_params): site = super().init_sites(model_params) al...

Ah I see. In that case you can replace the hopping for u1, u2, dx in self.lat.pairs['nearest_neighbors']: self.add_coupling(-t, u1, 'Bd', u2, 'B', dx, plus_hc=True) that generates \sum_{<i,j>} (b^\dagger_i b_j + hc) with for u1, u2, dx in self.lat.pairs['nearest_neighbors']: self.add_coupling(-t, u1...

If you want to extend the BH model without rewriting everything, you can do sth like class MyExtendedBHModel(tenpy.BoseHubbardModel): def init_terms(self, model_params): super().init_terms(model_params) gamma = model_params.get('gamma', 0, 'real_or_array') for u in range(len(self.lat.unit_cell)): se...

The term you want is called parity or 'P' in the BosonSite, with definition P = 1 - 2 (n \text{ mod } 2) = (-1)^n = \mathrm{exp}(\mathrm{i} \pi n) . So for H = \sum_i \gamma_i * \mathrm{exp}(\mathrm{i} \pi n_i) + H_\text{other} you could do something like def init_terms(self, model_params): ... # ot...

Have a look at these examples that simulate groundstate expectation values
https://tenpy.readthedocs.io/en/latest/ ... _dmrg.html

See https://github.com/tenpy/tenpy/pull/495 for functions that export tenpy objects (MPS or Hamitlonians from a model) to full matrix representations.

I assume you mean the Bose Hubbard model?
In what state do you want to take the expectation value?
If you want it in the groundstate, you can take an MPS psi resulting from DMRG and use
psi.expectation_value('N'), which gives you the particle number on every single site.

tenpy, with charge conservation has a basis order that might be surprising. See e.g. the warning in Site So I assume that you are writing down H_sp in an incompatible basis (probably you use {|up>, |down>}, and if you use charge conservation, tenpy will use {|down>, |up>}). Have a look at model.lat....

Confirmed that the workaround above works for my quick test.
For the fix see https://github.com/tenpy/tenpy/pull/481

Hi, Looks like this is bug in the consistency_check ecosystem, specifically for IrregularLattices. TeNPy tries to warn users if the lattice has too large N_sites_per_ring. This check causes an error, because N_sites_per_ring is None for the IrregularLattice. I will push a fix soon. In the meantime y...

Hi bart, just FYI that this will be resolved in the next version of tenpy, developed at https://github.com/tenpy/cyten. There, we consider this permutation in ``Tensor.to_numpy()`` such that it behaves as expected, i.e. such that ``.combine_legs(...).to_numpy()`` is equivalent to ``.to_numpy().resha...