Dear Matthias,

   my intention is doing finite T QMC for 2D ising in transverse field with the following Hamiltonian:
   H=-J \Sigma_{i,j} S_{i}^{z} S_{j}^{z}-h \Sigma_{i} S_{i}^{x}
   but for checking the accuracy of the numeric I did some checks for 1D case which we can have an exact results,
   probably I am expecting too much accuracy, for example:
  
    L=100, T=0.32859
     Exact::  E(T)=-105.29789708270407,   Mx(T)=0.27030367598168420
     looper::  E(T)=-105.61795 (0.00554),   M(T)=0.4093185 (0.000138) ( I think it is in z direction)
     with  SWEEPS:6000000, THERMALIZATION=2000000

     I have checked also for other sizes and very large SWEEPS.
    I don't expect to get exact result but I need much more accuracy in the calculated energy.

     and also other question: that magnetization which looper calculates is in the z direction?
     can I also measure M_{x} just with declaring it in parm file?
  
     Thanks a lot,
      Zhian.


On Sat, Jul 23, 2011 at 12:00 PM, <comp-phys-alps-users-request@lists.phys.ethz.ch> wrote:
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Today's Topics:

  1. restarting Lanczos iteration (jessica.alfonsi@unipd.it)
  2. Quantum Monte Carlo for Ising in transvers field (zhian asadzadeh)
  3. Re: Quantum Monte Carlo for Ising in transvers field
     (Matthias Troyer)
  4. Re: restarting Lanczos iteration (Matthias Troyer)


----------------------------------------------------------------------

Message: 1
Date: Fri, 22 Jul 2011 12:22:47 +0200
From: jessica.alfonsi@unipd.it
Subject: [ALPS-users] restarting Lanczos iteration
To: comp-phys-alps-users@lists.phys.ethz.ch
Message-ID:
       <5b0ae17b0813c63a97720e0fbc6cc1c6.squirrel@webmail.unipd.it>
Content-Type: text/plain;charset=utf-8

Hi all,
I'd like to modify the Lanczos *.cpp examples in IETL example folder to be
able to restart the iteration from any interruption point during the
Lanczos iteration. I suppose first one has to dump some information, for
instance the cofficients of T-matrix and the starting vector, however the
more difficult part would be the resuming of the iteration. Can somebody
give me some hints on how accomplishing this task? Thanks in advance...

Best regards,

Jessica Alfonsi





------------------------------

Message: 2
Date: Fri, 22 Jul 2011 13:03:23 +0200
From: zhian asadzadeh <zhian.asadzadeh@gmail.com>
Subject: [ALPS-users] Quantum Monte Carlo for Ising in transvers field
To: comp-phys-alps-users@lists.phys.ethz.ch
Message-ID:
       <CAEw6G6vLtP2G8kviZ97cxgZy9Dv1x_MqyUzFWs9ejnM8WvwnmA@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Dear All,

I am trying to do QMC at finite temperature for calculating the
magnetization of *Ising model in transverse field*, but I realized just
looper code is working for this model, ( the others codes doesn't work with
off diagonal matrix elements) but the result are not so good.
I am interested to modify dirloop_sse for this model, is it possible?
I appreciate your help,
Thanks,
zhian.
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Message: 3
Date: Fri, 22 Jul 2011 09:09:43 -0600
From: Matthias Troyer <troyer@phys.ethz.ch>
Subject: Re: [ALPS-users] Quantum Monte Carlo for Ising in transvers
       field
To: comp-phys-alps-users@lists.phys.ethz.ch
Message-ID: <A3A66CE8-DA3B-4160-8952-42868D25C5AC@phys.ethz.ch>
Content-Type: text/plain; charset="iso-8859-1"

Dear Zhian,

What is the problem with the looper code? It should be perfect for a nonfrustrated Ising model in a transverse field. What is your model?

Best regards

Matthias



On 22 Jul 2011, at 05:03, zhian asadzadeh wrote:

> Dear All,
>
> I am trying to do QMC at finite temperature for calculating the magnetization of Ising model in transverse field, but I realized just looper code is working for this model, ( the others codes doesn't work with off diagonal matrix elements) but the result are not so good.
> I am interested to modify dirloop_sse for this model, is it possible?
> I appreciate your help,
> Thanks,
> zhian.

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Message: 4
Date: Fri, 22 Jul 2011 09:35:31 -0600
From: Matthias Troyer <troyer@phys.ethz.ch>
Subject: Re: [ALPS-users] restarting Lanczos iteration
To: jessica.alfonsi@unipd.it, comp-phys-alps-users@lists.phys.ethz.ch
Message-ID: <F50F2D14-EF41-4772-A2F8-8C0533C8A54F@phys.ethz.ch>
Content-Type: text/plain; charset=us-ascii

Hi Jessica,

Resuming iterations is already possible now. The Lanczos algorithm allows you to continue iterating with a new iteration object. In your case I would not iterate until convergence but only for a fixed number of steps.

Indeed, all you have to store are the member variables of the Lanczos (and underlying T-matrix) object, as well as the two last vectors of the iteration (not the starting vector!). It is not hard to add that.

Matthias



On 22 Jul 2011, at 04:22, jessica.alfonsi@unipd.it wrote:

> Hi all,
> I'd like to modify the Lanczos *.cpp examples in IETL example folder to be
> able to restart the iteration from any interruption point during the
> Lanczos iteration. I suppose first one has to dump some information, for
> instance the cofficients of T-matrix and the starting vector, however the
> more difficult part would be the resuming of the iteration. Can somebody
> give me some hints on how accomplishing this task? Thanks in advance...
>
> Best regards,
>
> Jessica Alfonsi
>
>
>



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