Search found 32 matches

by QichengTang
18 Sep 2019, 03:32
Forum: HowTos and FAQ for TeNPy
Topic: correlation length in idmrg
Replies: 1
Views: 1206

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: 28311

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: 28311

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: 2755

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: 2518

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: 2518

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: 2518

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: 2518

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: 2518

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: 1878

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: 1878

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: 1473

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: 1473

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: 2638

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: 2242

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,...
by QichengTang
31 Jan 2019, 14:16
Forum: HowTos and FAQ for TeNPy
Topic: How to generate a random MPS in tenpy
Replies: 5
Views: 2242

Re: How to generate a random MPS in tenpy

Thanks for your reply. But what i'm looking for is not a random product state. What I want is a general state not a product state. I konw that there is a method to obtain a random state by a random unitary evolution process, but i'm asking a more simple way to get a random state, like by using some ...
by QichengTang
29 Jan 2019, 15:48
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 2638

Re: Scaling of entanglement entropy for iDMRG

I mean, in iDMRG, the boundary condition is like a periodic boundary condition. So, your problem is you use the wrong formula, you should use a formula for periodic boundary condition when you do an iDMRG calculation. In a finite case, you can choose open boundary condition or periodic, but in tenpy...
by QichengTang
29 Jan 2019, 14:22
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 2638

Re: Scaling of entanglement entropy for iDMRG

hi, i believe the reason is that in iDMRG the boundary condition is like a periodic boundary condition.
Your formula is for the open boundary condition, and for periodic boundary condition this should be c/3 but not c/6.
I recommend you to read the following two ref: arXiv:hep-th/0405152 and arXiv:0905.4013.
by QichengTang
21 Jan 2019, 13:49
Forum: HowTos and FAQ for TeNPy
Topic: How to generate a random MPS in tenpy
Replies: 5
Views: 2242

How to generate a random MPS in tenpy

how to generate a random MPS? Is the function "npc.Array.from_func" helpful?
PS. I think it's worthy to add a function like "rand_mps".
by QichengTang
17 Jan 2019, 15:18
Forum: HowTos and FAQ for TeNPy
Topic: the truncation in dmrg
Replies: 5
Views: 2122

Re: the truncation in dmrg

Okay, I see. I'm wrong about the truncation protocol in tenpy.
But, it's still kind of weird for me, I mean, the value of 1.e-10 ("svd_min") is a very small number, it should not influence the result, or I'm wrong with some very trivial things?
by QichengTang
17 Jan 2019, 06:56
Forum: HowTos and FAQ for TeNPy
Topic: the truncation in dmrg
Replies: 5
Views: 2122

Re: the truncation in dmrg

Thanks for your reply, I know that the problem maybe the degeneracy of the ground state, but that's not my point. My point is, I thought only one of these parameters "svd_min", "trunc_err", "max_bond" for truncation works. I mean I thought there is a protocol to choose ...
by QichengTang
08 Jan 2019, 03:36
Forum: HowTos and FAQ for TeNPy
Topic: the truncation in dmrg
Replies: 5
Views: 2122

the truncation in dmrg

I think the following finding should be noticed by everyone who uses tenpy. When I run dmrg for xxz chian, I found that the result will be strongly dependents on the parameter "svd_min", and this doesn't make sense. I have run the following test to show the problem. I'm confused, what may ...