New release: v0.7.1.

Search found 185 matches

by Johannes
23 Sep 2020, 08:21
Forum: HowTos and FAQ for TeNPy
Topic: finite open, finite periodic and infinite periodic chains
Replies: 5
Views: 1522

Re: finite open, finite periodic and infinite periodic chains

Yes, the MPS is still finite and OBC-style bc_MPS='finite' , with vectors at the boundary. It's just that the couplings in the MPO are topolically equivalent to a ring, as you drew it in your picture. Using the "default" order wouldn't change this, you would still need to define the MPS to have bc_M...
by Johannes
22 Sep 2020, 07:39
Forum: HowTos and FAQ for TeNPy
Topic: Bond dimension is not increasing
Replies: 1
Views: 35

Re: Bond dimension is not increasing

You set n_max=1, i.e. you consider hard-core bosons with at most 1 particle per site, and the model has particle number conservation. The product state from which you initialize is completely filled with one particle per site, such that the hopping term can't contribute - it would create one hole an...
by Johannes
21 Sep 2020, 14:43
Forum: HowTos and FAQ for TeNPy
Topic: New to tenpy
Replies: 2
Views: 93

Re: New to tenpy

Take a look at the overview and readthe other "introductions". You want to use the tenpy.models.hubbard.FermiHubbardModel with the tenpy.models.lattice.Ladder (for the other ladders, implement your own "Lattice" class as described in the various introductions). The t,U,L are model parameters in TeNP...
by Johannes
21 Sep 2020, 12:55
Forum: Releases
Topic: Release v0.7.0 and v0.7.1
Replies: 0
Views: 68

Release v0.7.0 and v0.7.1

Version 0.7.0 and 0.7.1 have been released about 2 weeks ago and are available from pip and conda. Before updating , please read at least the section incompatible changes of the changelog. The highlight of the changes is the new support for time evolution with the W_{II} method for approximating the...
by Johannes
21 Sep 2020, 10:14
Forum: HowTos and FAQ for TeNPy
Topic: Loschmidt Echo
Replies: 2
Views: 99

Re: Loschmidt Echo

Welcome! The MPS which you pass to the TEBDEngine gets modified in place (because we want to avoid unnecessary copies of MPS in case they are large). In other words, psi_0 and eng.epsi are the same MPS (namely the time evolved one). The solution is to make a copy of the MPS at some point, e.g. psi_0...
by Johannes
02 Sep 2020, 16:54
Forum: HowTos and FAQ for TeNPy
Topic: finite open, finite periodic and infinite periodic chains
Replies: 5
Views: 1522

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 that you unde...
by Johannes
24 Aug 2020, 09:26
Forum: HowTos and FAQ for TeNPy
Topic: Possible bug to implement vanishing coupling strength?
Replies: 2
Views: 243

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...
by Johannes
21 Aug 2020, 09:51
Forum: HowTos and FAQ for TeNPy
Topic: Bosonic Haldane Model
Replies: 1
Views: 179

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...
by Johannes
20 Aug 2020, 09:29
Forum: HowTos and FAQ for TeNPy
Topic: Qn about iDMRG
Replies: 2
Views: 238

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, ...
by Johannes
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: 321

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 ...