## Search found 337 matches

- 22 Sep 2022, 09:09
- Forum: HowTos and FAQ for TeNPy
- Topic: 01_dmrg.ipynb but with periodic boundary conditions
- Replies:
**2** - Views:
**67**

### Re: 01_dmrg.ipynb but with periodic boundary conditions

Indeed, the issue is that the periodic boundary conditions induce a long-range coupling in the model. (The MPS is still open, but I think you already got this.) You don't even need to define a custom model, since there is also the tenpy.models.tf_ising.TFIModel , which is the same as the TFIChain ex...

- 31 Aug 2022, 09:40
- Forum: HowTos and FAQ for TeNPy
- Topic: Linking MKL issue in window 11
- Replies:
**1** - Views:
**114**

### Re: Linking MKL issue in window 11

Looks like it's installed correctly, even if HAVE_MKL was not set on compile time. It's able to load the compiled parts, so no need to worry, all good! If TeNPy is compiled without HAVE_MKL, it falls back to the BLAS functioncs of numpy and scipy, and as fas as I know, numpy+scipy on Windows actuall...

- 31 Aug 2022, 09:32
- Forum: HowTos and FAQ for TeNPy
- Topic: Varying Lattice Spacing
- Replies:
**2** - Views:
**159**

### Re: Varying Lattice Spacing

If the "long range" coupling has a finite range, i.e. you put a cutoff of say 5 sites or so, and don't include any coupling afterwards, you can indeed just call add_exponentially_decaying_coupling a bunch of times with corresponding distances. If you want a "true" long range coup...

- 31 Aug 2022, 08:38
- Forum: HowTos and FAQ for TeNPy
- Topic: Why does my SSH model not working
- Replies:
**1** - Views:
**109**

### Re: Why does my SSH model not working

You're using a FermionChain. As the name suggests, the FermionChain has as local sites the tenpy.networks.site.FermionSite . This site doesn't define "up" or "down" states, but only "full" and "empty" states. Try to adjust the initial product state to be e.g. ...

- 17 Aug 2022, 16:49
- Forum: Implementations
- Topic: Implementing TEBD of open quantum chain in TenPy.
- Replies:
**1** - Views:
**214**

### Re: Implementing TEBD of open quantum chain in TenPy.

Hi Sourav, cool, great to hear that you want to implement this in TeNPy! There's different ways to implement Lindblad evolution, so before we discuss TeNPy, we should maybe discuss a bit which way you want to implement it, and it's probably much easier to do this over zoom. I'll contact you by email...

- 17 Aug 2022, 15:39
- Forum: HowTos and FAQ for TeNPy
- Topic: Converting MPS to State Vector
- Replies:
**2** - Views:
**220**

### Re: Converting MPS to State Vector

Formally yes , you can do it by just contracting all the tensors of the MPS, leaving the physical legs open. Depending on your preferred form, you might want to combine the L physical legs of dimension d into a single, big leg of dimension dim(\mathcal{H})= d^L , but this is essentially just a resh...

- 10 Aug 2022, 16:30
- Forum: HowTos and FAQ for TeNPy
- Topic: Regarding Two point correlation function in TenPy
- Replies:
**2** - Views:
**201**

### Re: Regarding Two point correlation function in TenPy

In general, you should probably do this for one j in the center of your chain only and write this as C(t) = \langle \psi_0 | e^{i H t} S^z_i e^{-iHt} S^z_j | \psi_0 \rangle = \langle \psi(t) | S^z_i | \phi(t) \rangle, \quad \text{where} \quad |\psi(t) \rangle = e^{-iHt} |\psi_0 \rangle \text{~and~} ...

- 10 Aug 2022, 16:08
- Forum: HowTos and FAQ for TeNPy
- Topic: UserWarnings differ for identical initializations when run several times
- Replies:
**1** - Views:
**284**

### Re: UserWarnings differ for identical initializations when run several times

That's expected behaviour given the implmentation of these warnings. The engine does use the options, but only once you actually time evolve the state with eng.run() . This stems from the convention that options only need to be read out by the time when they are actually used: depending on previousl...

- 29 Jul 2022, 10:21
- Forum: HowTos and FAQ for TeNPy
- Topic: My correlation functions from MPS.correlation_function and MPSEnvironment.expectation value disagree
- Replies:
**2** - Views:
**216**

### Re: My correlation functions from MPS.correlation_function and MPSEnvironment.expectation value disagree

The issue is confusion about the (first two) arguments of correlation_function . Giving a list of operators as arguments does not mean that you evaluate correlations between multi-site terms, but that you evaluate different correlation functions on even vs odd sites: psi.correlation_function(['A','B...

- 29 Jul 2022, 07:09
- Forum: HowTos and FAQ for TeNPy
- Topic: Crash during calculation of <Sy>
- Replies:
**4** - Views:
**297**

### Re: Crash during calculation of <Sy>

Glad to hear that

- 27 Jul 2022, 16:25
- Forum: HowTos and FAQ for TeNPy
- Topic: Crash during calculation of <Sy>
- Replies:
**4** - Views:
**297**

### Re: Crash during calculation of <Sy>

I checked, and the code runs without issues on my machine. I'd guess it's some incompatibility/issue with the BLAS code being called in the end. First of all, try whether it works with export TENPY_OPTIMIZE=0 , which forces TeNPy to not load the compiled Cython parts. How did you install TeNPy? Did ...

- 26 Jul 2022, 16:26
- Forum: HowTos and FAQ for TeNPy
- Topic: Spin-Boson MPO
- Replies:
**1** - Views:
**271**

### Re: Spin-Boson MPO

Hi, and sorry for the slow response; I hope it's still useful, given that I added extensive examples and further functions! Let me first explain why your examples do or don't work: When you write the MPO grid as W_0 = (S^z, S^x); W_1 = (N, N^2)^T or as in the last example, The [tenpyclass=tenpy.netw...

- 22 Jul 2022, 08:40
- Forum: HowTos and FAQ for TeNPy
- Topic: term_correlation_function_left for MPSEnvironment
- Replies:
**3** - Views:
**387**

### Re: term_correlation_function_left for MPSEnvironment

You can also do SpIdSm = tenpy.networks.site.kron(s.Sp, s.Id, S.Sm, group=False) The tenpy.networks.site.kron function with n input onsite operators generates an operator acting on n consecutive sites at once, with n input and n output legs, e.g for n=3, p0*, p1*, p2*, p0, p1, p2 . The expectation_v...

- 19 Jul 2022, 10:22
- Forum: HowTos and FAQ for TeNPy
- Topic: reset environment
- Replies:
**1** - Views:
**206**

### Re: reset environment

Since you fully re-initialize the TwoSiteDMRGEngine in the example you sent without passing the environment, you actually don't reuse the environment here. You define a new (random) product_state , but don't use it to initialize psi itself, I assume you also do that within the loop? And what exactly...

- 19 Jul 2022, 09:55
- Forum: HowTos and FAQ for TeNPy
- Topic: term_correlation_function_left for MPSEnvironment
- Replies:
**3** - Views:
**387**

### Re: term_correlation_function_left for MPSEnvironment

Really, the proper functions is to adjust the *correlation_function methods of the MPS to the MPSEnvironment, see the new 173 . If you really just need the nearest-neighbor correlations, the expectation_value actually supports this: import tenpy s = tenpy.networks.site.SpinHalfSite() psi = tenpy.net...

- 18 Jul 2022, 16:09
- Forum: HowTos and FAQ for TeNPy
- Topic: Hermitian conjugate for coupled system
- Replies:
**1** - Views:
**214**

### Re: Hermitian conjugate for coupled system

The first example adds terms b^\dagger_{x,0} b_{x,1} n_{x+1,1} + b^\dagger_{x,1} b_{x,0} n_{x+1,0} , which is not hermitian due to the switch in the n index. DMRG (or more precisely the Lanczos called by DMRG) always assumes a hermitian Hamiltonian! The "poorly conditioned Lanczos" is like...

- 18 Jul 2022, 15:48
- Forum: HowTos and FAQ for TeNPy
- Topic: Cell choice and long range correlations in a 2D iDMRG calculation
- Replies:
**2** - Views:
**249**

### Re: Cell choice and long range correlations in a 2D iDMRG calculation

If you expect translation invariance along the cylinder direction (and you Hamiltonian itself is also translation invariant in x-direction), Lx=1 is certainly a natural choice. Using Lx=1 does not hinder the calculation of correlation lengths - in general, if you have an infinite MPS, it just implie...

- 18 Jul 2022, 15:11
- Forum: HowTos and FAQ for TeNPy
- Topic: Different Energy measures giving mixed results
- Replies:
**1** - Views:
**183**

### Re: Different Energy measures giving mixed results

TEBD breaks translation invariance by performing the Trotterization of the evolution operator onto even/odd bonds. The direct way to reduce this effect is to do more, but smaller timesteps. You could also try to do higher-order evolution, but of course that doesn't make your algorithm higher-order i...

- 18 Jul 2022, 14:42
- Forum: HowTos and FAQ for TeNPy
- Topic: Newcomer of tenpy having an issue with my code
- Replies:
**1** - Views:
**267**

### Re: Newcomer of tenpy having an issue with my code

It's correct behaviour that the state doesn't change: You start from the fully polarized all-up state, which is an eigenstate of the Hamiltonian! Try to start from another initial state, e.g. the Neel state: product_state = ["up", "down"] psi = MPS.from_product_state(M.lat.mps_si...

- 17 Jun 2022, 12:17
- Forum: Implementations
- Topic: Why can we set a low number of maximal Lanczos iterations in DMRG?
- Replies:
**0** - Views:
**384**

### Why can we set a low number of maximal Lanczos iterations in DMRG?

Actually, I have a few more questions for you about lanczos in TeNPy. I notice that in TeNPy you set the default maximum number of iterations for lanczos (i.e. the attribute N_max) to be 20. However, when I tried to realize DMRG and lanczos algorithm on my own, I found that for a Hermitian matrix w...

- 17 Jun 2022, 12:02
- Forum: HowTos and FAQ for TeNPy
- Topic: add_multi_coupling vs. GroupedSite
- Replies:
**4** - Views:
**610**

### Re: add_multi_coupling vs. GroupedSite

What bond dimensions did you try for the timing benchmarks? I'd expect it to become relevant only around chi >~500 or so, maybe even just with chi on the order of a thousands.

- 10 Jun 2022, 19:01
- Forum: HowTos and FAQ for TeNPy
- Topic: Linking against MKL
- Replies:
**1** - Views:
**377**

### Re: Linking against MKL

It's documented in the conda-forge docs here . I think that's actually fine and properly linked against mkl. I've checked, and when I start from a fresh conda environment defined by TeNPy's environment.yml, I also get the # All requested packages already installed. Indeed, when I checked the install...

- 10 Jun 2022, 16:16
- Forum: HowTos and FAQ for TeNPy
- Topic: add_multi_coupling vs. GroupedSite
- Replies:
**4** - Views:
**610**

### Re: add_multi_coupling vs. GroupedSite

Of course, both approaches can work and should give similar results eventually; but I'd usually recommend not grouping sites if you can manage to write the model without grouping. Let me elaborate: When using the tenpy.networks.site.GroupedSite , you will double your local Hilbert space dimension d ...

- 10 Jun 2022, 15:24
- Forum: HowTos and FAQ for TeNPy
- Topic: How to apply a quantum channel?
- Replies:
**2** - Views:
**405**

### Re: How to apply a quantum channel?

I'm confused - what state do you start with? Some ground state, or other pure state, represented as an MPS? What do you want to calculate afterwards? You can use TeNPy to get the single-site reduced density matrix, and then apply the dephasing channel, but you can not apply it on the whole MPS: it's...

- 01 Jun 2022, 13:50
- Forum: HowTos and FAQ for TeNPy
- Topic: About the entropy growth in random unitary circuit
- Replies:
**2** - Views:
**439**

### Re: About the entropy growth in random unitary circuit

With the random unitary evolution, you get an ensemble of Haar-distributed states, i.e. each normalized state has the same probability. Since there *are* states with less than maximal, but no states with more-than-maximal entropy, it is clear that the average entropy in the Haar distribution is less...