## Search found 32 matches

- 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...

- 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.

- 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_{...

- 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.

It's not hard to modify the code, and I think this is necessary.

- 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...

- 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...

- 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...

- 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...

- 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...

- 20 Apr 2019, 17:13
- Forum: Algorithms
- Topic: question about tdvp
- Replies:
**2** - Views:
**1878**

- 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...

- 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.

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.

- 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...

- 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...

- 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,...

- 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 ...

- 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...

- 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.

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.

- 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".

PS. I think it's worthy to add a function like "rand_mps".

- 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?

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?

- 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 ...

- 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 ...