## Search found 329 matches

- 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:
**60**

### 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:
**57**

### 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:
**57**

### 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:
**139**

### 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:
**197**

### 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:
**73**

### 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:
**197**

### 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:
**94**

### 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:
**99**

### 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:
**75**

### 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:
**106**

### 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:
**223**

### 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:
**374**

### 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:
**237**

### 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:
**374**

### 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:
**259**

### 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:
**301**

### 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...

- 30 May 2022, 10:40
- Forum: HowTos and FAQ for TeNPy
- Topic: 1d lattice with arbitrary distribution of sites
- Replies:
**1** - Views:
**328**

### Re: 1d lattice with arbitrary distribution of sites

Hi Umberto, there is a tenpy.models.lattice.TrivialLattice , which is exactly the approach 1) you described - it just takes a list of sites, and defines them as a single, big unit cell. Internally in TeNPy, this is used if you group sites together, since you then no longer have the original lattice ...

- 30 May 2022, 10:23
- Forum: HowTos and FAQ for TeNPy
- Topic: Alternating Heisenberg coupling at infinite chain
- Replies:
**4** - Views:
**429**

### Re: Alternating Heisenberg coupling at infinite chain

I don't see the issue here, I checked that it works for an even number of couplings , where the couplings are not incommensurable. For nearest neighbor couplings A_i B_{i+1}, this means it works for (finite, odd # sites) or (infinite, even # sites), as you can easily check with the example below. No...

- 03 May 2022, 15:10
- Forum: HowTos and FAQ for TeNPy
- Topic: Alternating Heisenberg coupling at infinite chain
- Replies:
**4** - Views:
**429**

### Re: Alternating Heisenberg coupling at infinite chain

Hi,

yes, that is correct. It works if the number of couplings is even (ie. odd number of sites for finite systems, even number of sites for infinite MPS) , otherwise it complains about incommensurate arrays for the expansion.

yes, that is correct. It works if the number of couplings is even (ie. odd number of sites for finite systems, even number of sites for infinite MPS) , otherwise it complains about incommensurate arrays for the expansion.

- 26 Apr 2022, 17:07
- Forum: HowTos and FAQ for TeNPy
- Topic: calculate four-point correlation function
- Replies:
**1** - Views:
**240**

### Re: calculate four-point correlation function

Yes, you can do better. The explicit loops you have make this scale as O(L^3 \chi^3) , since each call to psi.expectation_value_term is O(|j+1 - i| \chi^3) . You can get this down to O(L^2 \chi^3) by using the term_correlation_function_right or ..._left, with term_L = [('Cd', 0), ('Cd', 1)], term_R=...

- 21 Apr 2022, 02:01
- Forum: HowTos and FAQ for TeNPy
- Topic: Charge Info for Z3 symmetry in 3-state Potts Model
- Replies:
**3** - Views:
**477**

### Re: Charge Info for Z3 symmetry in 3-state Potts Model

TeNPy tries to preserve local, diagonal symmetries, in your case the Z3 symmetry (\sum_i Q_i \mod 3) where Q_i = diag(0, 1, 2) are the charge values you define. However, the Hamiltonian does not preserve these symmetries, since the \Gamma^{(1,2)}_i don't commute with this symmetry. Instead, you need...

- 18 Apr 2022, 17:18
- Forum: HowTos and FAQ for TeNPy
- Topic: iDMRG sweep schedule
- Replies:
**3** - Views:
**501**

### Re: iDMRG sweep schedule

1) These additional sweeps are meant to (i) bring the MPS into canonical form and (ii) converge the environments. Effectively, it's mostly SVDs and environment updates, and usually cheap compared to the Lanczos optimization, so it should be "cheap" to converge things a bit better, even if ...

- 18 Apr 2022, 17:02
- Forum: HowTos and FAQ for TeNPy
- Topic: parallel computing
- Replies:
**4** - Views:
**719**

### Re: parallel computing

The export OMP_NUM_THREADS=1 is a bash command. You should have a slurm/sge/bash script which you submit to the cluster, include this line there. For example, if you use the setup of the TeNPy project repository , you can explicitly add the corresponding line in the file cluster_templates/slurm.sh (...

- 04 Apr 2022, 17:43
- Forum: HowTos and FAQ for TeNPy
- Topic: TDVP time evolution with interaction / onsite state probability
- Replies:
**2** - Views:
**430**

### Re: TDVP time evolution with interaction / onsite state probability

Indeed, the get_probability is not working; it even gives you wrong dimensions of the array when you go beyond 2 sites. Using the onsite reduced density matrix is as pointed out in the post you linked to is indeed one way. Another and maybe even clearer solution would be to define projection operato...