Search found 426 matches
- 28 Jun 2019, 09:25
- Forum: HowTos and FAQ for TeNPy
- Topic: DMRG sweep problems
- Replies: 5
- Views: 6260
Re: DMRG sweep problems
This jumping sure looks very wrong and strange. Any chance you could provide a simple example code where this happens? Do you expect a (nearly) degenerate ground state in this case? Than it might just be jumping around between different solutions. It might help to use 'chi_list' to gradually increas...
- 28 Jun 2019, 08:48
- Forum: HowTos and FAQ for TeNPy
- Topic: Some questions about the svd_theta
- Replies: 7
- Views: 7970
Re: Some questions about the svd_theta
Hi Qicheng, how exactly do you want to extract the correlation length from the B? For a finite system, this is a somewhat ill-defined question, because you have no (guaranteed) periodicity. You might want to look at the correlation functions directly and fit an exponential to that. For an infinite s...
- 28 May 2019, 20:07
- Forum: HowTos and FAQ for TeNPy
- Topic: periodic conditions
- Replies: 7
- Views: 6466
Re: periodic conditions
Exactly as in the example you posted: just specify an array/list as "strength" in add_coupling. In fact, you don't even need to define your own model, if you're happy with the XXZ Chain /SpinChain with alternating strength: from tenpy.models.xxz_chain import XXZChain model_params = { 'bc_M...
- 28 May 2019, 08:34
- Forum: HowTos and FAQ for TeNPy
- Topic: periodic conditions
- Replies: 7
- Views: 6466
Re: periodic conditions
Welcome! The first argument of add_coupling is the strenght of the coupling. It can be a single value (if the strength is uniform all over the chain/lattice), but also a numpy array or something convertible a numpy array (which is the case here). The different values just indicate that the strength ...
- 15 May 2019, 13:47
- Forum: Releases
- Topic: Release v0.4.0
- Replies: 0
- Views: 17992
Release v0.4.0
Version 0.4.0 has been released. Before updating , please read the release notes . It is now supported to install TeNPy with pip via pip install --upgrade physics-tenpy # for 'stable' versions I'd recommend an installation with pip if you do not intend to modify the source files of TeNPy at any poin...
- 07 May 2019, 13:28
- Forum: HowTos and FAQ for TeNPy
- Topic: add_coupling in SpinModel
- Replies: 4
- Views: 4535
Re: add_coupling in SpinModel
These operators do not commute here because they are acting on the same site. \sigma_i and \tau_i certianly do commute, which is obvious if you don't think in the grouped-site picture. In other terms, your hamiltonian is \begin{align} H &= J \sum_{<i,j>} (\sigma^x_i \sigma^x_j + \sigma^y_i \sig...
- 06 May 2019, 13:52
- Forum: HowTos and FAQ for TeNPy
- Topic: add_coupling in SpinModel
- Replies: 4
- Views: 4535
Re: add_coupling in SpinModel
Writing this with Hermitian conjugates, I get: J_x S^x_i S^x_j + J_y S^y_i S^y_j = \left( \frac{J_x + J_y}{4} \right)(S^+_i S^-_j + (S^+_j S^-_i)^\dagger) + \left( \frac{J_x - J_y}{4} \right)(S^+_i S^+_j + (S^+_j S^+_i)^\dagger) Sorry, but I disagree. Using h.c. it reads: J_x S^x_i S^x_j + J_y S^y_...
- 03 May 2019, 14:54
- Forum: HowTos and FAQ for TeNPy
- Topic: How to get the data of NPC arrays
- Replies: 1
- Views: 2801
Re: How to get the data of NPC arrays
The _data attribute of an tenpy.linalg.np_conserved.Array is a list with individual blocks of the tensor. Even without charges, there can be subblocks defined. this is the case for an MPO to exploit the sparseness of an MPO - if you write the Matrix, there are usually lot's of zeros, e.g. in your ca...
- 29 Apr 2019, 16:14
- Forum: HowTos and FAQ for TeNPy
- Topic: Cython compilation error
- Replies: 5
- Views: 6699
- 29 Apr 2019, 13:54
- Forum: HowTos and FAQ for TeNPy
- Topic: Cython compilation error
- Replies: 5
- Views: 6699
Re: Cython compilation error
Did you do the
Or in other words, do you have a working C++ compiler?
sudo apt-get install build-essential
?Or in other words, do you have a working C++ compiler?
- 29 Apr 2019, 09:27
- Forum: HowTos and FAQ for TeNPy
- Topic: Cython compilation error
- Replies: 5
- Views: 6699
Re: Cython compilation error
This looks like a linking error. What OS are you using? Can you compile the first minimal example from http://docs.cython.org/en/latest/src/quickstart/build.html? Another minimal example with numpy: save this code as "a.pyx". cimport numpy as cnp import numpy as np cnp.import_array() def m...
- 23 Apr 2019, 08:47
- Forum: Implementations
- Topic: Triangular Lattice
- Replies: 4
- Views: 14985
Re: Triangular Lattice
Implemented
- 19 Apr 2019, 09:34
- Forum: HowTos and FAQ for TeNPy
- Topic: Memory saving options in dmrg
- Replies: 2
- Views: 3470
Re: Memory saving options in dmrg
unfortunately, this is currently not implemented in TeNPy :( What you need to do is to write a custom tenpy.networks.mpo.MPOEnvironment which stores the tensors to disk instead of keeping them in the _LP and _RP lists. It should suffice to overwrite the get_LP, get_RP, set_LP, set_RP , del_LP, del_R...
- 18 Apr 2019, 15:55
- Forum: HowTos and FAQ for TeNPy
- Topic: Interpenetrating Lattices
- Replies: 2
- Views: 3082
Re: Interpenetrating Lattices
Currently, there is nothing to directly support this in TeNPy. What you need to do is implement your own lattice (as a subclass of tenpy.models.lattice.Lattice ). Example: import numpy as np from tenpy.models import lattice from tenpy.networks import site class MyLattice(lattice.Lattice): def __init...
- 18 Apr 2019, 13:02
- Forum: Implementations
- Topic: Triangular Lattice
- Replies: 4
- Views: 14985
Re: Triangular Lattice
Agreed. The Triangular lattice is basically just a simple square lattice with one of the basis vectors rotated by 30 degrees towards the other. I'd suggest to use basis = np.array([[0.5 *np.sqrt(3), 0.5], # first basis vector [0., 1.]]) # second basis vector: y-direction If you quickly write down th...
- 17 Apr 2019, 14:21
- Forum: HowTos and FAQ for TeNPy
- Topic: Performing TEBD for NNN interactions
- Replies: 1
- Views: 2870
Re: Performing TEBD for NNN interactions
Currently, the swapping for TEBD is not supported, although it should not be too difficult to implement, following the way you have outlined. There are a few things to be careful about, though: You need to adjust the existing model code to get the exponentials of the NNN terms. avoid onsite terms ap...
- 17 Apr 2019, 13:43
- Forum: HowTos and FAQ for TeNPy
- Topic: Suggestions for computing entanglement eigenvectors
- Replies: 2
- Views: 3025
Re: Suggestions for computing entanglement eigenvectors
What exactly do you mean by computing the entanglement eigenvectors? The eigenvectors of which matrix? For a finite system, I could imagine to look at individual Schmidt vectors (=singular vectors) on the left or right of a given cut in the form of an MPS. You can obtain them by just the part of the...
- 17 Apr 2019, 13:35
- Forum: HowTos and FAQ for TeNPy
- Topic: correlation length and charge sector
- Replies: 1
- Views: 2605
Re: correlation length and charge sector
Good question, thanks for pointing that out. The dominant eigenvector with eigenvalue 1 should always be in 0 charge sector: in canonical form the dominant eigenvector is just the identity, which has no charge. But I agree that it is not clear a priori (at least not to me) in which sector the next t...
- 28 Mar 2019, 11:07
- Forum: HowTos and FAQ for TeNPy
- Topic: TF Ising Magnetization issues
- Replies: 2
- Views: 4048
Re: TF Ising Magnetization issues
Short answer : Try measuring correlation functions, or expectation values of |M| or M^2 instead of M=\sum_i X_i ;) Reason : You try to observe spontaneous symmetry breaking. By definition, spontaneous symmetry meaking means that you have a degenerate ground state (in the thermodynamic limit): the s...
- 22 Mar 2019, 10:02
- Forum: HowTos and FAQ for TeNPy
- Topic: How to implement boundary pinning field in iDMRG appropriately?
- Replies: 2
- Views: 3430
Re: How to implement boundary pinning field in iDMRG appropriately?
In iDMRG, the iMPS unit cell is the central part of a growing environment on the left and right. The idea of the Engine.init_env() is to re-use the environment (and state) from a previous run. If the state has a sufficiently large correlation length, the environmnet "pins" DMRG to find the...
- 14 Mar 2019, 15:10
- Forum: Other News
- Topic: Serious bug in models
- Replies: 0
- Views: 47580
Serious bug in models
Another serious bug, this time in the models.
The problem is/was that adding the hermitian conjugate with was not done correctly.
Further details at issue #23.
If you have implemented your own model, check that you do it correctly in your case
The problem is/was that adding the hermitian conjugate with was not done correctly.
Further details at issue #23.
If you have implemented your own model, check that you do it correctly in your case
- 13 Mar 2019, 13:54
- Forum: Other News
- Topic: Serious bug in npc.inner
- Replies: 0
- Views: 17983
Serious bug in npc.inner
I found a serious bug in npc.inner . This bug could result in wrong expecation values and Lanczos/DMRG giving completely wrong results. Luckily, the bug was only on the github master branch for two weeks (since March 02), so I hope it didn't cause too many problems yet. In case you did a "git p...
- 13 Mar 2019, 09:23
- Forum: HowTos and FAQ for TeNPy
- Topic: Finite DMRG not working after update to new version
- Replies: 4
- Views: 4906
Re: Finite DMRG not working after update to new version
Sorry, that's indeed true. The bug only appeared if you use a mixer and have a model without onsite terms.
Should be fine now
PS: You can also report problems like that as github issues.
Should be fine now
PS: You can also report problems like that as github issues.
- 12 Mar 2019, 17:29
- Forum: HowTos and FAQ for TeNPy
- Topic: Finite DMRG not working after update to new version
- Replies: 4
- Views: 4906
Re: Finite DMRG not working after update to new version
I recently changed the order of axes in DMRG from (vR.p1) to (p1.vR) to avoid unnecessary transposes. However, the newest version should consistently use "(p1.vR)". Did you actually store some MPS (e.g. with pickle) and load it again? Or do you restart the whole simulation/initialization o...
- 06 Mar 2019, 10:18
- Forum: HowTos and FAQ for TeNPy
- Topic: Exponentiation of operator / String order parameter
- Replies: 11
- Views: 100190
Re: Exponentiation of operator / String order parameter
I just noticed an error in my last post above, see the edit. I hope that was clear anyways...