Dear Matthias,
1. I congratulate you and your colleagues for creating such a fantastic tool as ALPS is.
2. See point 1.
3. Still there is a lot of truth in what Khalid Hassan wrote. To be specific:
- I cannot go to Zurich for personal consultation. Both from Paris where I am on sabbatical and from Krakow (POland) it is a bit too far just for asking a couple of simple questions.
Instead I go to Tutorial and Documentation link on https://alps.ethz.ch/mediawiki/index.php/Main_Page
and want to read about:
Definition of custom measurements or Common hardcoded measurements
to know what I can get. But these sections of the Documentation are EMPTY.
So I guess from examples .. but I cannot guess everything. To be specific. I run QMC codes for Bose-Hubbard. I know how to get occupation at different sides (for inhomogenous model, e.g. with harmonic trap and/or disorder), call them <n_i>. But I am interested in second moment <n_i^2>
What I can do?
a/ I wrote a long email to you b/ 2 times I posed questions on the very same subject on this list
without getting any answer. From more experienced colleague, I learn that I may modify qmc.h so I get <n_i^2> INSTEAD of <n_i> - but this requires recompilation of applications and running the whole simulation twice.
There MUST be a more intelligent way of getting the info I need.
Or correlations <a_i a_j^\dagger> or <n_i n_j> ....
May somebody give an advice on that?
4. Simon Trebst was happy that you reached 100 citations to ALPS (I guess this is both to old and new reference). I bet you, were there more user friendly documentation available and more active list of users, the number of citations would increase tremendously... I am sure that at least by 1 since the things we work on now (with ALPS) could be finished in a more reasonable ammount of time...
All the best Jakub
Message: 2 Date: Thu, 26 Mar 2009 20:19:22 -0700 From: Matthias Troyer troyer@phys.ethz.ch
Dear Khalid Loane,
The ALPS libraries are meant to be used in user code, and are documented. The applications had been designed as black box codes. However, if you would like to learn more about them and work on one of
them, we will be delighted to help. Best would be a personal visit though to explain the code structure - and clean it up while doing that.
Matthias
On 26 Mar 2009, at 14:12, khalid hassan wrote:
alps is a program that works well with a comprehensive help. but if
one has use its code for one self research, the code provides little
help. it has very few comments and difficult to understand. Can there can be any help for the code of full diagonalization for example logical structure, flow chart, algorithm available. If this
is in personal files of the developers can they send by email or if
someone visits them they can give him.
Best Regards Khalid Loane ITCP, Graz Austria
End of Comp-phys-alps-users Digest, Vol 36, Issue 15
Dear Jakub,
So I guess from examples .. but I cannot guess everything. To be specific. I run QMC codes for Bose-Hubbard. I know how to get occupation at different sides (for inhomogenous model, e.g. with harmonic trap and/or disorder), call them <n_i>. But I am interested in second moment <n_i^2>
There is a solution which looks ugly, but works :
patch the definition of the site basis of the model you're working with. In your example, Bose-Hubbard Hamiltonian uses the basis called "boson". Go to models.xml file and then add a line to the SITEBASIS definition:
<SITEBASIS name="boson"> <PARAMETER name="Nmax" default="infinity"/> <QUANTUMNUMBER name="N" min="0" max="Nmax"/> <OPERATOR name="bdag" matrixelement="sqrt(N+1)"> <CHANGE quantumnumber="N" change="1"/> </OPERATOR> <OPERATOR name="b" matrixelement="sqrt(N)"> <CHANGE quantumnumber="N" change="-1"/> </OPERATOR> <OPERATOR name="n" matrixelement="N"/> <OPERATOR name="n2" matrixelement="N*N"/> <!-- added --> </SITEBASIS>
Like I said, it's ugly, but it works. And, like you, I'd be very much interested in learning how to add measurements properly, without dirty tricks :).
Best,
Zhenya
comp-phys-alps-users@lists.phys.ethz.ch