TeNPy Forum

Hang on - you're running DMRG to obtain ground states, right? What do you mean with the "evolution" steps? Why do you need the GroupedSite at all, if you're only running DMRG? Can you specify the hamiltonian? And the transfer matrix between which states? You might need to explicitly set ch...

Version 0.6.0 and 0.6.1 have been released. Before updating , please read at least the section incompatible changes of the changelog. Most important changes The release of v0.6.0 contains a major update of the documentation, which is now hosted by "Read the Docs" at https://tenpy.readthedo...

You're right of course. Okay, let me just say that I never tried it... You should probably still make sure that you follow the evolution with \theta adiabatically. In other words, use the result from the DMRG run with \theta as an initial guess for the \theta + \delta \theta DMRG, similarly as is do...

So you try to use torus boundary conditions now? Just to make sure, the correct way to do this is (whith the standard toric code model as in the Repo): from tenpy.networks.mps import MPS from tenpy.algorithms import dmrg from tenpy.models.toric_code import ToricCode def example_run_TC(): model_param...

I don't think this works, even for finite MPS or with exact diagonalization. The issue is that you need to pin the phase of the ground state, which is not well defined from the perspective of a variational algorithm: if |\Psi\rangle is a ground state, so is e^{i \phi} |\Psi\rangle , so any variation...

By the way, you don't have to modify the model inside the tenpy repo for that, you can do something like this: from tenpy.models import toric_code from tenpy.models.lattice import IrregularLattice class MyToricCode(toric_code.ToricCode): def init_lattice(self, model_params): reg_lat = super().init_l...

Sorry, that was a small bug. I've fixed it in 037ad76272825bf6f4de1a72fb4e5529a1fcdec9.

I'm not sure what's the problem here? The chiral_pi_flux.py example does work directly in the thermodynamic limit with infinite MPS. Running it generates chiral_pi_flux_charge_pump.pdf , the equivalent of Fig. 4 in the paper you quote, and chiral_pi_flux_ent_spec_flow.pdf , the equivalent of Fig. 8....

It's simply psi_1.overlap(psi_2) , or for the normalization as in your formula, psi_1.overlap(psi_2)/psi_1.norm / psi_2.norm . See overlap for more details. For infinite MPS, it's the largest eigenvalue of the transfermatrix, which is not just the overlap <psi_1|psi_2> - the latter is zero for any t...

Sorry if that wasn't clear. It's not included in version 0.6.1 on pip yet, but it's on the github master branch. So you need to install the latest version from github. With pip: pip uninstall physics-tenpy # if you installed it before pip install git+git://github.com/tenpy/tenpy.git or download the ...

Just for your information, this is now possible in the latest version of TeNPy with the help of the tenpy.models.lattice.IrregularLattice, see example in it's docstring and https://tenpy.readthedocs.io/en/latest/ ... tices.html

This is now resolved, see https://tenpy.readthedocs.io/en/latest/ ... r-lattices

Let me understand what you want to do. Do you want to write down a fully-2D PEPS where each tensor has 5 legs, left, right,up, down, physical? And then you somehow extract a single row/column of the PEPS as an MPS, with "dangling" legs (for a row, dangling up and down indices) to apply TEB...

First of all: I've updated the documentation on Monday and added a completely new user-guide page describing many details on lattices , including a small section on irregular hattices on the end. Moreover, I've added some examples in the doc-string of the tenpy.models.lattice.IrregularLattice itself...

1.) The toric code model acutally didn't allow for that, you would have had to override the init_lattice method. I've just updated it in 4cc12c0ab9f38cc970da7e5338a1ee3210964997 to allow torus-boundary conditions with bc_MPS="finite", bc_x="periodic", bc_y="periodic" . ...

Wow, someone interested in the methods of that paper :) Sorry for the bad programming style making it hard to use it without TEBD :? The BackwardsDisentangler needed full access to TEBD, and I wanted to have a uniform interface for the different disentangler classes. Copy/paste works, of course. Alt...

TEBD does work for non-hermitian hamiltonians since the commit closing the issue. DMRG does right now not work in this case, since it uses Lanczos which crucially assumes that the hamiltonian is hermitian. You would need to use a different eigensolver for non-hermitian H, and I have now idea how wel...

You want to cut the system into two halves, but get_rho_segment extracts the density matrix for the *few* sites you give as argument, so that's the wrong function. The equations from the cited paper is really what's calculated by average_charge of the MPS (up to the prefactor constants, I believe), ...

Having one more up than down electron can only work if you have an odd number of sites. Then you can do, e.g, initial_state = ["up", "down"] * (M.lat.N_sites // 2) initial_state.append("up") If you have an even number of sites and want two more up than down electrons, ...

Thanks for pointing it out, I've updated it on the master branch.
Unfortunately, it didn't make it into the release of v0.6.0 any more, which I packed last Friday

1) It depends on the physical system, not just the lattice! E.g. in the dimer lattice of my previous post, you should define the ordering such that each dimer is nearest-neighbor in the MPS. 3.) The order you plotted here is different from the default one of the tenpy.models.lattice.Honeycomb lattic...

In the latest version of the master branch, the function definitely has the labels arguments, introduced in 8dd1f93b719074770a9d6cef16f0d89d9fd6229d on Jan. 27th. This change was introduced after the last official release of v0.5.0 on Dez.18 last year, however, so if you used the pip install physics...

The square lattice of Leon Balents' paper is a 45-degree rotation compared to the DualSquareLattice we are using. This implies a different geometry for the cylinder axis (going in the [1, 1] direction of our DualSquareLattice), and a different "cut" when you split the MPS between unit cell...

Yes, that's almost right. We're working on something like this in the exp_MPO branch on github. It's not quite ready for use, and we will adjust the interface to better match the other evolution algorithms, but it basically works as a preliminary version, and you can look at it to see how it works. ...

1) TeNPy only supports "open" MPS, since peridoic MPS don't have a canonical form. You can make your Model have periodic/toric boundary conditions and still have an open MPS, and TeNPy supports that. The price you pay is that you need the squared bond dimension due to the (expected) entang...