Search found 32 matches

by QichengTang
02 Apr 2020, 05:39
Forum: HowTos and FAQ for TeNPy
Topic: Question about generating random MPS
Replies: 1
Views: 3842

Question about generating random MPS

Hi everyone, I'm trying to generate a random MPS by using the example in test module of tenpy (see the end of this post). I found that when L > 140, it will raise RuntimeError: SVD found no singluar values. I'm not sure where I make wrong, does anyone know something about this? thanks, Qicheng def r...
by QichengTang
12 Mar 2020, 08:07
Forum: HowTos and FAQ for TeNPy
Topic: leading eigenvector of transfer matrix
Replies: 6
Views: 5094

Re: leading eigenvector of transfer matrix

You cannot/should not take the transfer matrix of a single site, if you have a two-site unit cell in your MPS. Sometimes, the charge values will not even allow you, and even if they do, it there is a different gauge on the two bonds - which can and will be the case if there are degenerate singular ...
by QichengTang
11 Mar 2020, 04:32
Forum: HowTos and FAQ for TeNPy
Topic: leading eigenvector of transfer matrix
Replies: 6
Views: 5094

Re: leading eigenvector of transfer matrix

BTW, in this sense, the normalization factors of the left (to square singular value) and right eigenvector (identity) of right canonical form should cancel each other out, right? However, in a real case it seems will change the largest amplitude of the transfer matrix (the largest eigenvalue will b...
by QichengTang
11 Mar 2020, 03:48
Forum: HowTos and FAQ for TeNPy
Topic: leading eigenvector of transfer matrix
Replies: 6
Views: 5094

Re: leading eigenvector of transfer matrix

It's just a matter of normalization. Eigenvalues get normalized to np.linalg.norm(v) = 1 , but in this case you want np.sum(v) = 1 . At the end of your code, add vdiag = v.diagonal() print(vdiag/np.sum(vdiag)) print(psi.get_SL(0)**2) and compare the results, the prints should give the same Thanks f...
by QichengTang
10 Mar 2020, 13:48
Forum: HowTos and FAQ for TeNPy
Topic: leading eigenvector of transfer matrix
Replies: 6
Views: 5094

leading eigenvector of transfer matrix

Hi everyone, it is well known that, in left(right) canonical form infinite MPS, the leading left(right) eigenvector (corresponding to eigenvalue 1) of the transfer matrix is a unit matrix \mathbb{1} , and the leading right(left) eigenvector is \lambda^2 \mathbb{1} . However, when I trying to test th...
by QichengTang
10 Mar 2020, 06:47
Forum: HowTos and FAQ for TeNPy
Topic: Real-time evolution of the GS of the U=0 Fermi-Hubbard model
Replies: 5
Views: 3900

Re: Real-time evolution of the GS of the U=0 Fermi-Hubbard model

Yes, that's for sure a good idea. Indeed, I thought about it and started to implement it already a few days ago, but I'm quite busy these days (moving to UC Berkeley :)), so I didn't have time to finish it. Hopefully, I can find a bit time next week - unless you volunteer to time to implement it ;-...
by QichengTang
14 Nov 2019, 03:02
Forum: HowTos and FAQ for TeNPy
Topic: Real-time evolution of the GS of the U=0 Fermi-Hubbard model
Replies: 5
Views: 3900

Re: Real-time evolution of the GS of the U=0 Fermi-Hubbard model

it is a good idea to write a function to evaluate the variance of H, and maybe something like |<\psi|H|\psi>|^2 - <\psi|H^2|\psi> can be used in dmrg to be a control parameter? What order (second or fourth) and timestep do you use for TEBD? Does this go away if you simply use a smaller timestep/high...
by QichengTang
01 Oct 2019, 03:14
Forum: HowTos and FAQ for TeNPy
Topic: print msg into file
Replies: 6
Views: 3446

Re: print msg into file

Thanks for your help Johannes, I actually do not know how to deal with this problem for a long time (not just for tenpy, also other code written by myself or others).
by QichengTang
26 Sep 2019, 12:05
Forum: HowTos and FAQ for TeNPy
Topic: print msg into file
Replies: 6
Views: 3446

Re: print msg into file

maybe i didnot explain my point clearly enough. The point is to save the printing msg in terminal at time . If simply use python3 abc.py > log the printing msg will be saved after the task is done, i.e. during running of the task, you can not read the msg in this log file. In the case of using a pyt...
by QichengTang
18 Sep 2019, 03:32
Forum: HowTos and FAQ for TeNPy
Topic: correlation length in idmrg
Replies: 1
Views: 1443

correlation length in idmrg

Hi, everyone. I'm trying to calculate the correlation length for TFI chain near or away from the critical point. I have test before, the calculated correlation length for critical point g=1 is agree with the pervious numeric presented by Frank Pollmann https://journals.aps.org/prl/abstract/10.1103/P...
by QichengTang
18 Sep 2019, 03:22
Forum: HowTos and FAQ for TeNPy
Topic: how to write a three-site interaction?
Replies: 4
Views: 28735

Re: how to write a three-site interaction?

Thanks for your explanation, Umberto. It's very clear.
by QichengTang
05 Sep 2019, 00:46
Forum: HowTos and FAQ for TeNPy
Topic: how to write a three-site interaction?
Replies: 4
Views: 28735

how to write a three-site interaction?

Hi everyone, I'm confused how to write a three-site interaction? I have read the example of toric code, but I donnot understand. If I want to write a O’Brien-Fendley model H=\sum_{j=1}^N [-\sigma^z_{j}\sigma^z_{j+1}-\sigma^x_{j}+\lambda(\sigma^x_{j}\sigma^z_{j+1}\sigma^z_{j+2}+\sigma^z_{j}\sigma^z_{...
by QichengTang
04 Sep 2019, 07:14
Forum: HowTos and FAQ for TeNPy
Topic: print msg into file
Replies: 6
Views: 3446

print msg into file

I'm wondering if the msg can be printed into a log file?
It's not hard to modify the code, and I think this is necessary.
by QichengTang
02 Jul 2019, 13:51
Forum: HowTos and FAQ for TeNPy
Topic: Some questions about the svd_theta
Replies: 7
Views: 3112

Re: Some questions about the svd_theta

You can only split legs that were combined previously. In TeNPy, you can see that those legs store the charge data as tenpy.linalg.charges.LegPipe instead of tenpy.linalg.charges.LegCharge . Those pipes have the additional data needed to split the legs. The matrices generated by SVD, say A_ij = U_i...
by QichengTang
02 Jul 2019, 13:29
Forum: HowTos and FAQ for TeNPy
Topic: Some questions about the svd_theta
Replies: 7
Views: 3112

Re: Some questions about the svd_theta

Thank you, Johannes, now I'm clear with the svd process, but here appears another question. As in the note said, the process of combination of two legs is something like mapping the indices for "vL" and "p" into something like "2*vL+p", so you can split out the physical...
by QichengTang
01 Jul 2019, 04:16
Forum: HowTos and FAQ for TeNPy
Topic: Some questions about the svd_theta
Replies: 7
Views: 3112

Re: Some questions about the svd_theta

There's another thing related, and I donnot understand how to deal with it. For example, consider a spin-half chain with conserved Sz, we can write down the 3 sub-blocks with Sz "-2, 0, 2", In this case, we can do svd for each charge sector. But in the case of, for example, TFI chain where...
by QichengTang
28 Jun 2019, 17:27
Forum: HowTos and FAQ for TeNPy
Topic: Some questions about the svd_theta
Replies: 7
Views: 3112

Re: Some questions about the svd_theta

Johannes, Thanks for your reply, I know that the transfer matrix method is only well-defined in a case with translational invariance, and for the contracting of the transfer matrix we need right matrice B or left matrice A. My question is about the implementation of the charge conservation in the ca...
by QichengTang
28 Jun 2019, 06:18
Forum: HowTos and FAQ for TeNPy
Topic: Some questions about the svd_theta
Replies: 7
Views: 3112

Some questions about the svd_theta

Hi everyone, I want to write a little program to calculate the correlation length with a given "theta" (which is located in the center of the chain), so I need to do svd to theta and get the right matrice B. But there is a problem, I get the theta by using function "get_theta" fo...
by QichengTang
20 Apr 2019, 17:13
Forum: Algorithms
Topic: question about tdvp
Replies: 2
Views: 2297

Re: question about tdvp

mpsforphysics, thx for you reply!

The lecture note arXiv:1810.07006 is very good!
by QichengTang
08 Apr 2019, 09:18
Forum: Algorithms
Topic: question about tdvp
Replies: 2
Views: 2297

question about tdvp

Hi, everyone. I'm trying to do tdvp, but there are something in the original paper which I cannot understand. Firstly, why the projector in this form? I know the projector is something like 1 - \sum_N |\psi_N><\psi_N| , but what's the target space here, it seems like we project it onto a basis orort...
by QichengTang
08 Mar 2019, 10:50
Forum: HowTos and FAQ for TeNPy
Topic: Product state results
Replies: 3
Views: 1817

Re: Product state results

I believe it's easy to generate a random product state with a given total charge.
for example, for qubit, it's just a combination of 0 and 1 with a given sum of all elements in the list, you just need to give the number of 0 and 1, and do a random permutation.
by QichengTang
27 Feb 2019, 10:07
Forum: HowTos and FAQ for TeNPy
Topic: Product state results
Replies: 3
Views: 1817

Re: Product state results

I will ask you the question what Johannes asked me: What the "random" state means here? It should be noticed that the charge (quantum number) should be conserved in dmrg, so if your random state has a different total charge, the result will be wrong. Perhaps you can use "RandomUnitary...
by QichengTang
22 Feb 2019, 09:34
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 3269

Re: Scaling of entanglement entropy for iDMRG

hi, everyone. I have to admit i was wrong, and what Umberto said is correct: The original formula is correct, and in infinite dmrg the boundary condition is open. BTW, bart, your scaling method may be wrong. Why you choose the data from a state which is not converged in dmrg? What I remember is: you...
by QichengTang
09 Feb 2019, 13:30
Forum: HowTos and FAQ for TeNPy
Topic: How to generate a random MPS in tenpy
Replies: 5
Views: 2742

Re: How to generate a random MPS in tenpy

Thanks for your reply! In fact, I want to get some states with random entanglement entropy. I know the random unitary time evolution will be a good method. I was thinking about that is there a method can directly obtain these states? The first coming problem is about the charge conserve as you said,...