Search found 426 matches
- 11 Mar 2021, 00:50
- Forum: HowTos and FAQ for TeNPy
- Topic: RuntimeWarning and how to fix it
- Replies: 3
- Views: 2642
Re: RuntimeWarning and how to fix it
Hi Ruben, I have seen this warning before as well, but not so much lately. I vaguely remember that I also tried printing the S values and/or checking that none of them was 0 or negative, but couldn't quite pinpoint it.When testing S=S**-1. for different values like S = np.array([1.e-2, 1.e-15, 1.e-2...
- 25 Feb 2021, 07:06
- Forum: HowTos and FAQ for TeNPy
- Topic: How to define a infiniteT MPS under canonical ensemble
- Replies: 3
- Views: 2603
Re: How to define a infiniteT MPS under canonical ensemble
I played around with this a little bit. When you choose a smaller time step, the error gets smaller, it's O(dt). Further, I noticed that the error is coming from the state not being in canonical form: If you call psi.canonical_form_finite() right before measurements, at least this error is gone, as ...
- 11 Feb 2021, 23:05
- Forum: HowTos and FAQ for TeNPy
- Topic: np conserved module
- Replies: 3
- Views: 3264
Re: np conserved module
Why do you need the state Sx|psi> in the first place? As you know, S^x=0.5* (S^+ + S^-) and thus applying Sx to a state S|\psi\rangle with fixed Sz will give you a superposition of |\phi^\pm\rangle := S^\pm |\psi\rangle . In other words, S^x |\psi\rangle does not have a well defined Sz charge, and c...
- 11 Feb 2021, 02:20
- Forum: HowTos and FAQ for TeNPy
- Topic: Convergence Problem for Quantum Impurity Systems
- Replies: 2
- Views: 1915
Re: Convergence Problem for Quantum Impurity Systems
Sorry for the late reply. In general, I think DMRG should be suitable for such problems. I could understand that it fails for tiny/zero values of lambda, but for O(1) values of lambda it should definitely work. (In fact, I think that people have successfully used DMRG as an impurity solver for DMFT....
- 11 Feb 2021, 00:57
- Forum: HowTos and FAQ for TeNPy
- Topic: Excited states using tenpy
- Replies: 13
- Views: 9280
Re: Excited states using tenpy
I've update the model userguide to inclue a new section on this.
- 11 Feb 2021, 00:33
- Forum: HowTos and FAQ for TeNPy
- Topic: Two component Bose-Hubbard model
- Replies: 4
- Views: 5737
Re: Two component Bose-Hubbard model
Your code looks right. I would have done it basically the same way :) In the newest version of TeNPy, tenpy.networks.site.multi_sites_combine_charges is deprecated in favor of tenpy.networks.site.set_common_charges , you should call it with set_common_charges([siteA, siteB], 'independent') . This sh...
- 10 Feb 2021, 19:23
- Forum: HowTos and FAQ for TeNPy
- Topic: Excited states using tenpy
- Replies: 13
- Views: 9280
Re: Excited states using tenpy
Yes, any strength given to add_onsite, add_coupling, or add_multi_coupling can be an array, as documented in these functions.
Thus also Jv, is allowed to be a numpy array. The shape it needs to have depend on the boundary conditions and shape of your lattice.
- 09 Feb 2021, 22:00
- Forum: HowTos and FAQ for TeNPy
- Topic: Excited states using tenpy
- Replies: 13
- Views: 9280
Re: Excited states using tenpy
the line states = dmrg_params['orthogonal_to'] = [] creates a new list and assigns it to both the variable name states and dmrg_params['orthogonal_to'] . Remember, in Python everything is an "object", and your variables really are just references to objects. Inside the loop, you first crea...
- 05 Feb 2021, 18:33
- Forum: HowTos and FAQ for TeNPy
- Topic: TDVP run time issue
- Replies: 3
- Views: 2796
Re: TDVP run time issue
1) How did you try to install TeNPy? It looks like it's using a version installed with `pip` into the local home directory. Can you try to pip uninstall physics-tenpy and then try to re-install TeNPy? Moreover, the svd_gesvd hints that you're using a very old version of scipy? What python are you us...
- 05 Feb 2021, 17:23
- Forum: HowTos and FAQ for TeNPy
- Topic: Excited states using tenpy
- Replies: 13
- Views: 9280
Re: Excited states using tenpy
1) That was intentional, you need a new copy each time in the loop! After all, you want to have a list of 3 different states in the end. You might at most argue that it's a bad idea to "restart" the whole DMRG from scratch for the excited states, if we already found a ground state. But the...
- 05 Feb 2021, 03:17
- Forum: HowTos and FAQ for TeNPy
- Topic: How to define a infiniteT MPS under canonical ensemble
- Replies: 3
- Views: 2603
Re: How to define a infiniteT MPS under canonical ensemble
This wasn't implemented yet in TeNPy , as you have probably seen by the ToDo entry. However, since today, it is: 64cd7a3a690e80b2876fce48e79675f060b52ab7 ;) The function from_infiniteT_canonical gives you an initial density matrix with fixed particle number on the physical sector, i.e. the canonical...
- 04 Feb 2021, 22:37
- Forum: About the forum
- Topic: Forum rules
- Replies: 0
- Views: 92325
Forum rules
Welcome! This forum is meant to be a community place for both the users and developers of the Tensor Network Python (TeNPy) package. The source code of this package is available on github . The official documentation (generated from the latest source code) has also a user-guide section with some tu...
- 04 Feb 2021, 19:37
- Forum: HowTos and FAQ for TeNPy
- Topic: finite open, finite periodic and infinite periodic chains
- Replies: 10
- Views: 10874
Re: finite open, finite periodic and infinite periodic chains
Even though the model is originially nearest-neighbor on the periodic chain, it will have longer-range interactions in the (open-boundary) MPS - with default ordering, there is one interaction going from site 0 to site L-1, or if you use the "folded" order, most of the originally nearest-n...
- 04 Feb 2021, 19:22
- Forum: HowTos and FAQ for TeNPy
- Topic: Warning Cons_N and Cons_Sz unused
- Replies: 2
- Views: 2119
Re: Warning Cons_N and Cons_Sz unused
That's why the warning is there - to help you spot typos
- 04 Feb 2021, 19:22
- Forum: HowTos and FAQ for TeNPy
- Topic: Modified Fermi-Hubbard model
- Replies: 3
- Views: 3225
Re: Modified Fermi-Hubbard model
Well, TEBD is nice because it is conceptually very simple - you just use a Suzuki-Trotter decomposition and straight forward iterations of (apply two site gate; compress & split to get back to MPS form). Grouping sites makes things more costly, however - formally TEBD scales as \mathcal{O}(\chi^...
- 04 Feb 2021, 03:17
- Forum: HowTos and FAQ for TeNPy
- Topic: Create a hump-like density profile in Fermi-Hubbard model
- Replies: 1
- Views: 2928
Re: Create a hump-like density profile in Fermi-Hubbard model
First of all, let me clarify: Do you want some uniform "background density" and then some more particles in the center? Or do you only want particles in the center? For 1): If you don't enforce charge conservation, DMRG is "allowed" to switch to another charge sector, even if you...
- 04 Feb 2021, 02:49
- Forum: HowTos and FAQ for TeNPy
- Topic: Excited states using tenpy
- Replies: 13
- Views: 9280
Re: Excited states using tenpy
you need to make a loop and run DMRG multiple times, each time orthogonalizing against the previous state: psi0 = MPS.from_product_state(...) states = dmrg_params['orthogonal_to'] = [] for i in range(3): psi = psi0.copy() results = dmrg.run(psi, M, dmrg_params) states.append(psi) # this also adds th...
- 04 Feb 2021, 01:30
- Forum: HowTos and FAQ for TeNPy
- Topic: Entanglement_entropy for finite ladder
- Replies: 2
- Views: 2685
Re: Entanglement_entropy for finite ladder
Let's look at the example Ladder image: https://tenpy.readthedocs.io/en/latest/reference/tenpy-models-lattice-Ladder-1.png The MPS follows the red dashed line 0 - 1 - 2 -3 -4 -5- ... When you cut the MPS at the bond between 3 and 4, it will split the system in regions left = {0, 1, 2, 3} and right={...
- 04 Feb 2021, 01:11
- Forum: HowTos and FAQ for TeNPy
- Topic: Modified Fermi-Hubbard model
- Replies: 3
- Views: 3225
Re: Modified Fermi-Hubbard model
If you have at most next-nearest neighbor interactions in a 1D chain, you can group sites and then perform TEBD. In general, I'd recommend to switch to another time evolution algorithm, though: either TDVP or the tenpy.algorithms.mpo_evolution.ExpMPOEvolution can deal with longer range. The latter e...
- 04 Feb 2021, 01:06
- Forum: HowTos and FAQ for TeNPy
- Topic: DMRG with fixed bond dimension
- Replies: 2
- Views: 2019
Re: DMRG with fixed bond dimension
Welcome, Rike!
chi_min can only avoid reducing the bond dimension, not increase it further.
In addition to setting chi_min to the same value as chi_max, you should set svd_min to 0.
chi_min can only avoid reducing the bond dimension, not increase it further.
In addition to setting chi_min to the same value as chi_max, you should set svd_min to 0.
- 04 Feb 2021, 00:36
- Forum: HowTos and FAQ for TeNPy
- Topic: How to obtain full spectrum of given Model?
- Replies: 1
- Views: 2472
Re: How to obtain full spectrum of given Model?
Clearly, you can only do this for small system sizes, where you can also do a full exact diagonalization. DMRG really is not a good algorithm at finding excited states, as I explained in the earlier posting You should just use exact diagonalization to find (all) the excited states, and then convert ...
- 04 Feb 2021, 00:03
- Forum: HowTos and FAQ for TeNPy
- Topic: Basis for a fermion chain
- Replies: 1
- Views: 1549
Re: Basis for a fermion chain
I'm not sure what exactly you mean with "occupation-number-representation basis". You have a local basis of occupations, e.g. for spin-less fermions just |0\rangle, |1\rangle> = c^\dagger |0\rangle , or for spin-full fermions |0\rangle , |\uparrow\rangle \equiv c^\dagger_\uparrow|0\rangle,...
- 03 Feb 2021, 23:44
- Forum: HowTos and FAQ for TeNPy
- Topic: Relation between bond energies and total expected value of energy of MPS
- Replies: 1
- Views: 2235
Re: Relation between bond energies and total expected value of energy of MPS
You tried to find *all* possible eigenstates, right? Really, DMRG is not good at finding highly excited states - that's not what it is designed for ;) What fails is not the calculation of the energy, but the trick of finding excited eigenstates with an algorithm (DMRG) looking for the ground state. ...
- 02 Dec 2020, 21:00
- Forum: HowTos and FAQ for TeNPy
- Topic: Symmetries Of lattice
- Replies: 10
- Views: 7259
Re: Symmetries Of lattice
Sorry for the late reply; your post was displayed on another page that I didn't see. To see how you can use Sz conservation, take a look at the implementation of the tenpy.models.xxz_chain.XXZChain2 The lines self.add_coupling(Jxx * 0.5, u1, 'Sp', u2, 'Sm', dx, plus_hc=True) self.add_coupling(Jz, u1...
- 01 Dec 2020, 09:36
- Forum: HowTos and FAQ for TeNPy
- Topic: Entanglement spectrum by charge (specifically for iDMRG)
- Replies: 4
- Views: 4151
Re: Entanglement spectrum by charge (specifically for iDMRG)
Wow, I'm even mentioned in the acknowledgement
Thanks for coming back on this! It's great to see what people can do with TeNPy.
I've right away updated the list of papers citing TeNPy, your paper is now included
Thanks for coming back on this! It's great to see what people can do with TeNPy.
I've right away updated the list of papers citing TeNPy, your paper is now included