Search found 428 matches
- 02 Sep 2020, 16:54
- Forum: HowTos and FAQ for TeNPy
- Topic: finite open, finite periodic and infinite periodic chains
- Replies: 10
- Views: 10967
Re: finite open, finite periodic and infinite periodic chains
Oops! There was a bug in init_lattice that the 'order' parameter was read out, but not used for 1D lattices (i.e. the Chain and Ladder). I've quickly fixed this in 9e020640e180d6fb9d09f534a9c91fa047cf6bab . After this fix, using order='folded' is really "enough", apart from making sure tha...
- 24 Aug 2020, 09:26
- Forum: HowTos and FAQ for TeNPy
- Topic: Possible bug to implement vanishing coupling strength?
- Replies: 2
- Views: 2783
Re: Possible bug to implement vanishing coupling strength?
While it does not work with the version v0.6.1, it works with the latest version of the master branch. The fix is about a year old, but wasn't included into the master branch until recently when we merged the MPO evolution with the W_I/W_II approximations... I guess it's time for a version bump agai...
- 21 Aug 2020, 09:51
- Forum: HowTos and FAQ for TeNPy
- Topic: Bosonic Haldane Model
- Replies: 2
- Views: 2756
Re: Bosonic Haldane Model
You're right, that's a double counting. Good catch, thanks for pointing it out! The Fermionic Hofstadter model has the same problem, of course. Additionally, one of the example models had the issue. I've fixed it in a8448f36c23fda6f2ea8217f4f8e938acb7f67df bart Did you see this? Any other consequenc...
- 20 Aug 2020, 09:29
- Forum: HowTos and FAQ for TeNPy
- Topic: Qn about iDMRG
- Replies: 2
- Views: 25370
Re: Qn about iDMRG
The model is H = J \sum_{i} (0.5 (S^+_i S^-_{i+1} + h.c.) + \Delta S^z_I S^z_{i+1} ) - h^z \sum_i S^z_i , which is in the ferromagnetic phase of the XXZ chain for \Delta = -1.7 . In other words, the True ground state is simply all down states (or all up states, if you have a non-zero h^z ). Indeed, ...
- 31 Jul 2020, 13:11
- Forum: HowTos and FAQ for TeNPy
- Topic: DMRG different results using SingleSiteEngine and TwoSiteEngine and how to keep certain filling
- Replies: 1
- Views: 2527
Re: DMRG different results using SingleSiteEngine and TwoSiteEngine and how to keep certain filling
Imposing a small bond dimension has slightly different effects on single-site vs. two-site DMRG. Take the extreme case of chi=1, in which case single-site DMRG (without a mixer) effectively does mean-field theory for a single site in an environment, while two-site dmrg finds the ground state of two ...
- 31 Jul 2020, 10:59
- Forum: HowTos and FAQ for TeNPy
- Topic: Entanglement spectrum by charge (specifically for iDMRG)
- Replies: 4
- Views: 4165
Re: Entanglement spectrum by charge (specifically for iDMRG)
For infinite systems, the absolute value of the charges has no physical meaning but is a pure gauge choice; physical is only the difference between charge values. Indeed, the absolute value depends on the choice of your initial state - did you get different results when you initialized with the down...
- 11 Jul 2020, 04:20
- Forum: HowTos and FAQ for TeNPy
- Topic: Multiple sites to combine charges
- Replies: 1
- Views: 3146
Re: Multiple sites to combine charges
So you have 3 separate conserved quantities: number of A bosons siteA, number of bosons siteB, spin SiteZ? The charges for the siteA and siteB need to be different, so you can't pass the very same Site-instance. I expect the following to work: class BosonSin(CouplingMPOModel): def init_lattice(self,...
- 17 Jun 2020, 20:03
- Forum: HowTos and FAQ for TeNPy
- Topic: Superposition of MPS with different total charge
- Replies: 4
- Views: 6000
Re: Superposition of MPS with different total charge
To detect whether you have cat state, you should look at the eigenvalues of the transfermatrix, whether you get two eigenvalues exactly 1. If the ground state is a stripe, charge conservation can force it into superpositions. For that reason, I would also highly recommend to try using a larger (doub...
- 16 Jun 2020, 17:53
- Forum: HowTos and FAQ for TeNPy
- Topic: Superposition of MPS with different total charge
- Replies: 4
- Views: 6000
Re: Superposition of MPS with different total charge
(I took the freedom to slightly edit your suggested code.)
- 16 Jun 2020, 17:49
- Forum: HowTos and FAQ for TeNPy
- Topic: Superposition of MPS with different total charge
- Replies: 4
- Views: 6000
Re: Superposition of MPS with different total charge
May I ask why you want to create a superposition in the first place? Just for measurements? I don't really see a point for that. Or continuing some algorithm with another model which doesn't have the charge conservation? That would be more reasonable. Schollwoeck's 2011 review ("DMRG in the age...
- 16 Jun 2020, 05:29
- Forum: HowTos and FAQ for TeNPy
- Topic: Bipartitioning infinite MPS into 2 semi-infinite chains
- Replies: 11
- Views: 15055
Re: Bipartitioning infinite MPS into 2 semi-infinite chains
I see. Sorry, if I appeared rude; I just wasn't sure what you wanted to do. I'd still recommend running DMRG to find the ground state, which gives you an MPS, and then just take that as initial state for the TEBD, as outlined below. On a side note, you can derive your model directly from the Nearest...
- 15 Jun 2020, 16:41
- Forum: HowTos and FAQ for TeNPy
- Topic: Bipartitioning infinite MPS into 2 semi-infinite chains
- Replies: 11
- Views: 15055
Re: Bipartitioning infinite MPS into 2 semi-infinite chains
Why are you trying to do the time evolution? The paper you cited does *not* use TEBD, it uses DMRG! We define \theta = 2\pi t/T , assume adiabaticity and work in the instantaneous eigenbasis of H(\theta) . Hence, the charge transport becomes independent of the time scale T . "Adiabatically"...
- 15 Jun 2020, 16:14
- Forum: Algorithms
- Topic: Toy code for np_conservervation
- Replies: 1
- Views: 10601
Re: Toy code for np_conservervation
No, there is no toycode.
The idea is really just to keep track of the charges, which divides the tensor into smaller blocks, and multiply only the subblocks with compatible charges, re-implementing tensordot, eigh, ... to exploit the block structure.
The idea is really just to keep track of the charges, which divides the tensor into smaller blocks, and multiply only the subblocks with compatible charges, re-implementing tensordot, eigh, ... to exploit the block structure.
- 12 Jun 2020, 06:19
- Forum: HowTos and FAQ for TeNPy
- Topic: Bipartitioning infinite MPS into 2 semi-infinite chains
- Replies: 11
- Views: 15055
Re: Bipartitioning infinite MPS into 2 semi-infinite chains
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...
- 11 Jun 2020, 07:24
- Forum: Releases
- Topic: Release v0.6.0 and v0.6.1
- Replies: 0
- Views: 14238
Release v0.6.0 and v0.6.1
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...
- 10 Jun 2020, 01:13
- Forum: HowTos and FAQ for TeNPy
- Topic: overlap of ground states at different parameters
- Replies: 7
- Views: 9526
Re: overlap of ground states at different parameters
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...
- 10 Jun 2020, 01:05
- Forum: HowTos and FAQ for TeNPy
- Topic: entanglement_entropy_segment doubt
- Replies: 13
- Views: 15457
Re: entanglement_entropy_segment doubt
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...
- 10 Jun 2020, 00:37
- Forum: HowTos and FAQ for TeNPy
- Topic: overlap of ground states at different parameters
- Replies: 7
- Views: 9526
Re: overlap of ground states at different parameters
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...
- 10 Jun 2020, 00:10
- Forum: HowTos and FAQ for TeNPy
- Topic: Irregular lattice site removing doubt
- Replies: 4
- Views: 5118
Re: Irregular lattice site removing doubt
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...
- 10 Jun 2020, 00:00
- Forum: HowTos and FAQ for TeNPy
- Topic: Irregular lattice site removing doubt
- Replies: 4
- Views: 5118
Re: Irregular lattice site removing doubt
Sorry, that was a small bug. I've fixed it in 037ad76272825bf6f4de1a72fb4e5529a1fcdec9.
- 09 Jun 2020, 23:50
- Forum: HowTos and FAQ for TeNPy
- Topic: Bipartitioning infinite MPS into 2 semi-infinite chains
- Replies: 11
- Views: 15055
Re: Bipartitioning infinite MPS into 2 semi-infinite chains
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....
- 09 Jun 2020, 21:15
- Forum: HowTos and FAQ for TeNPy
- Topic: overlap of ground states at different parameters
- Replies: 7
- Views: 9526
Re: overlap of ground states at different parameters
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...
- 08 Jun 2020, 23:24
- Forum: HowTos and FAQ for TeNPy
- Topic: Adding a site to a chain perpendicularly
- Replies: 6
- Views: 8170
Re: Adding a site to a chain perpendicularly
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 ...
- 08 Jun 2020, 16:48
- Forum: HowTos and FAQ for TeNPy
- Topic: Adding a site to a chain perpendicularly
- Replies: 6
- Views: 8170
Re: Adding a site to a chain perpendicularly
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
- 04 Jun 2020, 01:26
- Forum: HowTos and FAQ for TeNPy
- Topic: Finite Chain with different unit cell at the beginning
- Replies: 4
- Views: 6432