dear all,

thanks for the responses, and sorry for the delay to reply. Yes, i was using the dmrg, and in fact using this new dmrg application `mps_optim`, as suggested by Michele Dolfi, solved my problem! I didn't know about this application, is there somewhere i can find a tutorial about it, or is it exactly the same input's as dmrg? And just a last point, in this application can i measure some "four-point" correlations, like "cdag_m:c_{m+1}:cdag_n:c_{n+1}" ?

best regards,

Fernando.



-----------------------------------
Date: Thu, 12 Jun 2014 08:52:52 +0200
From: Michele Dolfi <dolfim@phys.ethz.ch>
To: comp-phys-alps-users@lists.phys.ethz.ch
Subject: Re: [ALPS-users] alternative fermion Hubbard
Message-ID: <52E3FD2A-60E3-4D48-8315-1ACDF7348498@phys.ethz.ch>
Content-Type: text/plain; charset="us-ascii"

Hi Fernando,

If you are using a recent version of ALPS, e.g. 2.2.0b3, you can use the new dmrg application `mps_optim`.

It works the same way as the `dmrg` application, but additionally allows you to measure correlation functions for i<j, which very often is good enough.
MEASURE_HALF_CORRELATIONS[

cdag_up c_up]="cdag_up:c_up"


Best regards,
Michele

--
ETH Zurich
Michele Dolfi
Institute for Theoretical Physics
HIT G 32.4
Wolfgang-Pauli-Str. 27
8093 Zurich
Switzerland

dolfim@phys.ethz.ch
www.itp.phys.ethz.ch

+41 44 633 78 56 phone
+41 44 633 11 15 fax





On Jun 12, 2014, at 2:08 AM, Ryo IGARASHI <rigarash@issp.u-tokyo.ac.jp> wrote:

> Hi, Fernando,
>
> Assuming that you use DMRG simulation since you specify 'MAXSTATES'.
>
>
> (2014/06/12 0:10), Fernando Iemini wrote:
>> I've using the ''alternative fermion Hubbard'' model, with open boundary
>> conditions, and analyzing its single-particle correlations, <cdag_up:c_up>.
>> I'm not being able however to compute these observables for larger
>> lattices, e.g., L=~160. I'm getting a "segmentation fault" message, does
>> anybody know why is happening this error, maybe due to memory? If so, what
>> would be good parameters in order to avoid it?
>>
>> Here is the script i'm using:
>>
>> LATTICE="open chain lattice"
>> MODEL="alternative fermion Hubbard"
>> CONSERVED_QUANTUMNUMBERS="N,Sz,Nup,Ndown"
>> N_total=160
>> Sz_total=0
>> Nup_total=80
>> Ndown_total=80
>> mu=0
>> t=1
>> NUMBER_EIGENVALUES=1
>> L=160
>> MAXSTATES=100
>> MEASURE_CORRELATIONS[cdag_up c_up]="cdag_up:c_up"
>> {U = 9.000000e-01,V=5.500000e-01,TRUNCATION_ERROR=1e-7}
>
> This is memory issue. The problem is that 'MEASURE_CORRELATIONS'
> collects all pair sites. Observing ~10000 measurements costs too much
> memory.
>
> Not tested, but I believe that you can avoid this issue by tweaking
> models.xml and lattices.xml. Change the name of some specific operator
> and just calculating between them.
>
> --
> Ryo IGARASHI, Ph.D.
> rigarash@issp.u-tokyo.ac.jp
> tel: 04-7136-5343, fax: 04-7136-3441
> OpenPGP fingerprint: BAD9 71E3 28F3 8952 5640  6A53 EC79 A280 6A19 2319
>