Search found 32 matches

by dorf
24 Nov 2023, 00:11
Forum: HowTos and FAQ for TeNPy
Topic: Difference between ExpMPOEvolution and TimeDependentExpMPOEvolution
Replies: 0
Views: 39411

Difference between ExpMPOEvolution and TimeDependentExpMPOEvolution

Hello, I am running some quantum annealing simulations for the transverse field Ising model. At t=0 the Hamiltonian is just the field term and at t=T it's only the Ising terms with linear interpolation in-between. So far I have been just looping over time steps and initialized a new model with sligh...
by dorf
18 Jul 2023, 23:09
Forum: Algorithms
Topic: How are periodic boundary conditions implemented?
Replies: 3
Views: 11879

Re: How are periodic boundary conditions implemented?

Hey, is there a reference that I should cite if I use the 'folded' ordering? Seems like a well-known trick, but I wonder who 'did it first'.
Thanks!
by dorf
18 Jul 2023, 23:06
Forum: HowTos and FAQ for TeNPy
Topic: Calculating Time Evolution Only Once
Replies: 4
Views: 7703

Re: Calculating Time Evolution Only Once

Thank you very much for your detailed answer. Makes sense! I will try using different jobs instead of using multiprocessing.
by dorf
17 Jul 2023, 15:28
Forum: HowTos and FAQ for TeNPy
Topic: Calculating Time Evolution Only Once
Replies: 4
Views: 7703

Re: Calculating Time Evolution Only Once

Hey Johannes, ok thanks! This is what I wanted to know. So you're saying the the contraction with the approximated U is much more expensive than building it, whic makes sense! Because I apply the 'same circuit' to many different states all the time, I thought about calculating all the approximated U...
by dorf
13 Jul 2023, 23:41
Forum: HowTos and FAQ for TeNPy
Topic: Calculating Time Evolution Only Once
Replies: 4
Views: 7703

Calculating Time Evolution Only Once

Hey, so I use the `ExpMPOEvolution` to time evolve some MPS. It takes a MPS and a model as an input. I want to time evolve many different MPS with the same Hamiltonian. Is there a way to only approximate the unitary time-evolution once and use it on the different states instead of recalculating it o...
by dorf
03 Apr 2023, 16:34
Forum: HowTos and FAQ for TeNPy
Topic: MPS as Square Matrices
Replies: 3
Views: 1586

Re: MPS as Square Matrices

So doing the above doesn't seem to work for me. I converged an MPS with variable bond dimension, and then fix chi_min=chi_max for a new run, using the MPS as initial state. However, the bond dimension won't change, because it immediately is converged without the bond dimension being changed (increas...
by dorf
29 Mar 2023, 04:36
Forum: HowTos and FAQ for TeNPy
Topic: MPS as Square Matrices
Replies: 3
Views: 1586

Re: MPS as Square Matrices

Hey Johannes, thanks for your reply. You are right. I am looking at an infinite system. Because even for iDMRG L>=2, I would like to construct a translationally invariant MPS for a single site. I calculate ground states over a range of parameters and would like to fix the form of the output MPS. So ...
by dorf
24 Mar 2023, 02:46
Forum: HowTos and FAQ for TeNPy
Topic: MPS as Square Matrices
Replies: 3
Views: 1586

MPS as Square Matrices

Hey,
is there a way I tell tenpy to compute a MPS that consists only of square matrices?
Thanks!
by dorf
10 Nov 2022, 03:57
Forum: HowTos and FAQ for TeNPy
Topic: ExpMPOEvolution.run() vs. update()
Replies: 2
Views: 1904

Re: ExpMPOEvolution.run() vs. update()

Thank you very much for your reply. So checking the source codes it seems I'd have to use the 'make_measurement()' method. However, I want to measure something like this at each time step: for t in range(num_time_steps): env = MPSEnvironment(psi_0, evol.psi) out[t] = env.expectation_value(op, sites)...
by dorf
20 Sep 2022, 22:32
Forum: HowTos and FAQ for TeNPy
Topic: ExpMPOEvolution.run() vs. update()
Replies: 2
Views: 1904

ExpMPOEvolution.run() vs. update()

Hello, I am calculating some expectation values for a range of time steps. I have some MPS psi_0 and the following evolution: evol_params = {'approximation': 'I', 'dt': 0.1, 'N_steps': 1} Let's say I want to calculate quantities at 100 time steps. What's the most efficient way of doing so? Should I ...
by dorf
19 Jul 2022, 22:25
Forum: HowTos and FAQ for TeNPy
Topic: term_correlation_function_left for MPSEnvironment
Replies: 3
Views: 2265

Re: term_correlation_function_left for MPSEnvironment

Dear Johannes, yes, I am using finite MPS. Thank you very much for opening up the issue on github. In my case it's actually not i+1, but actually i+2, because I am working on a ladder. I am actually not sure whether I understand why the example that you kindly provided works. So is it because you se...
by dorf
27 Jun 2022, 03:28
Forum: HowTos and FAQ for TeNPy
Topic: term_correlation_function_left for MPSEnvironment
Replies: 3
Views: 2265

term_correlation_function_left for MPSEnvironment

Hi, I want to calculate the expectation value \langle \psi| S_i^z S_{i+1}^z |\phi \rangle . Because the two MPS are different, I create a tenpy.networks.mps.MPSEnvironment . What is the best way to compute the above correlation function? For tenpy.networks.mps.MPS there is tenpy.networks.mps.MPS.ter...
by dorf
27 Jun 2022, 03:05
Forum: HowTos and FAQ for TeNPy
Topic: add_multi_coupling vs. GroupedSite
Replies: 4
Views: 2860

Re: add_multi_coupling vs. GroupedSite

You are right. I only benchmarked up to ~256 where it wasn't so significant.
Thanks again, for the input!
by dorf
16 Jun 2022, 05:27
Forum: HowTos and FAQ for TeNPy
Topic: add_multi_coupling vs. GroupedSite
Replies: 4
Views: 2860

Re: add_multi_coupling vs. GroupedSite

Thank you very much for the answer. I implemented both and the results match. The difference in computation time was not so significant (for now), so I might stick to grouped sites because, as you said, they are kind of 'prettier' and easier to handle when extracting correlation functions etc. Again...
by dorf
23 May 2022, 04:37
Forum: HowTos and FAQ for TeNPy
Topic: add_multi_coupling vs. GroupedSite
Replies: 4
Views: 2860

add_multi_coupling vs. GroupedSite

Hello, I have a unit cell with 2 FermionSite and I would like to implement a term like c^\dagger_{0, n+1}c^\dagger_{1, n+1}c_{1, n}c_{0, n} , where 0 and 1 are the sublattice indices and n runs over the unit cells. So something like a two-body hopping term (or can be thought of as a nearest neighbor...
by dorf
10 Dec 2021, 13:32
Forum: HowTos and FAQ for TeNPy
Topic: Periodic versus Open Boundary Conditions
Replies: 5
Views: 4520

Re: Periodic versus Open Boundary Conditions

Thank you very much for the quick update! I managed to reproduce the results with open boundary conditions for the 'folded' ladder, by reordering the expectations value. Next step is to try it out with the periodic boundary conditions. In the post you refer to you you write that you should set [tenp...
by dorf
08 Dec 2021, 13:23
Forum: HowTos and FAQ for TeNPy
Topic: Periodic versus Open Boundary Conditions
Replies: 5
Views: 4520

Re: Periodic versus Open Boundary Conditions

Dear Johannes,
Sorry, I had put this problem aside for a while. Anyway, thank you very much for your answer.

The 'folded' order is not yet implemented for the ladder system, right? Can I implement a custom order myself in the model that I built?

Best,
Niclas
by dorf
27 Oct 2021, 07:35
Forum: HowTos and FAQ for TeNPy
Topic: Periodic versus Open Boundary Conditions
Replies: 5
Views: 4520

Periodic versus Open Boundary Conditions

Hello, I want to compare a finite system that has a surface with it's 'bulk-counterpart'. Using first DMRG calculations and then time-evolving methods I calculated the excitation spectrum. The size of the finite system was large enough, and it worked out well. However, now I want to compare it to th...
by dorf
30 Aug 2021, 19:42
Forum: HowTos and FAQ for TeNPy
Topic: M1 compatibily
Replies: 1
Views: 2233

M1 compatibily

I recently switched to a computer running Apples new M1 chip. However, tenpy is not available for the M1 conda distribution. Should I just run it via Rosetta (Apple's Intel interface) or can we expect a M1 compatible package on conda any time soon? :)
by dorf
28 Jun 2021, 14:56
Forum: HowTos and FAQ for TeNPy
Topic: Custom (sum of) Operators
Replies: 3
Views: 2729

Re: Custom (sum of) Operators

Thank you very much for your reply and that new functionality! However, I didn't quite get how to construct the operator for two different sites. Reading the documentation it seems that I have to pass an array of strings to kron(), which will be translated into some local operators (e.g. 'Sz' for th...
by dorf
21 Apr 2021, 08:52
Forum: HowTos and FAQ for TeNPy
Topic: Custom (sum of) Operators
Replies: 3
Views: 2729

Custom (sum of) Operators

Hi, is there an easy way to make custom operators and apply them to a MPS via 'mps.apply_local_op()'? Let's say I want to apply S^x_i + S^y_i+1 - const*Id. Is there some functionality that I can construct this operator, give a name to it, and then apply it? The 'const' is evaluated at runtime, so de...
by dorf
02 Apr 2021, 12:54
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 9152

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Thank you very much for the additional information. This is super helpful! Best regards!
by dorf
01 Apr 2021, 18:49
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 9152

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Dear Johannes, thank you very much for your help. For the moment I'm fine working with finite systems, as well. I mostly started with iDMRG because I followed the rough description given in Sec. IV in this work: https://arxiv.org/pdf/1804.06811.pdf it is explicitly mentioned that an iDMRG ground sta...
by dorf
01 Apr 2021, 10:35
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 9152

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

So after a couple of tests, the problem described above persists to occur for many combinations of states. At each time point t of the evolution I want to initialize an MPSEnvironment for all j for <psi_0 | psi_j> with |psi_j> being the time evolved state at time t with |psi_j> = U S_j |psi_0>, to t...
by dorf
27 Mar 2021, 12:00
Forum: HowTos and FAQ for TeNPy
Topic: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder
Replies: 15
Views: 9152

Re: Dynamical spin Structure Factor/ Excitation Spectrum of Spin Ladder

Sorry for my late reply, I really appreciate the help. Below you find the traceback, after I called MPSEnvironment(psi_0, testpsi) with psi_0 being an iDMRG ground state to which applied 'Sz' to some site with mps.apply_local_op, and testpsi the output of ExpMPOEvolution where psi_0.apply_local_op(s...