Dear Michele,

Thank for your prompt response. The second one looks like what I am looking for; however what do you mean by it is not superfast? for example, if I am interested on a nearest neighbor correlation over all of a lattice, which is O(n) correlations, will you recommend this option or the default given correaltion measurement (O(n^2))?

Bests,
Amir

On Mon, Mar 9, 2015 at 1:57 PM, Michele Dolfi <dolfim@phys.ethz.ch> wrote:
Dear Amir,

Yes it is possible. Here you find the list of all parameters.
http://alps.comp-phys.org/static/mps_doc/parameters.html

What you can use is:
1) MEASURE_HALF_CORRELATIONS[Name] which measures all i<j. So just N*N/2 calculations.
2) MEASURE_LOCAL_AT where you can specify at which position you want to measure the observables. For example MEASURE_LOCAL_AT[My Correlation] = “cdag_up:c_up|(0,1),(0,2),(0,3),(0,4)” to measure at i=0 and j=1,2,3,4. Note that this kind of measurements won’t be super-fast.


Best regards,
Michele

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



On 09 Mar 2015, at 18:19, Amir M.Aghaei <amir.maghaei@gmail.com> wrote:

Hi,

I have gone through the tutorial and the mailing list archive but I was unable to find whether it is possible to measure the correlation only between some sites of the lattice under study, say about O(n) of possible correaltions not every possible 2 sites in the lattice which is about O(n^2) and is definitely a waste of calculations in my case. So, is there any way that I can give a list (of two sites) to the program? If not, can you think of a very easy workaround?
 
My main interest right now is the new DMRG MPS code, so even if there is any MPS specific technique that I can use I would be happy to hear about it.

Bests,
Amir