Hi Zhenya,
that trick is an unsupported and undocumented feature as you found out. I'll talk to Adrian about DMRG. INITIAL_SITE will not be useful there since with open boundary conditions you want it symmetric around the center, but we'll find a solution.
Matthias
On 26 Jan 2009, at 03:00, Evgeny Burovskiy wrote:
Thanks for the clarification!
And indeed, the INITIAL_SITE parameter is quietly ignored by dmrg..
I suppose there is more urgent work for you alps developers, but as a humble user, I'd dare begging you to implement this feature as soon as realistically possible. If one needs a valid use case, here it is: as soon as I try running dmrg for sensible system sizes, e.g. L=80, the dmrg sweeping takes 2--3 hours, while calculating a full correlation function takes rather 16--20 hours. As far as I'm concerned, being able to only calculate O(L) values for correlators would be very very much welcome--- at least if one needs to check the large-distance asymptotics of a certain correlator, e.g. to see whether it's a power law or an exponential. I further guess that I'm not the only one trying to use alps dmrg for calculating correlations, hence the effort of implementing the feature would be useful for at least a few current and future users.
And as a side request: would it be possible to add a note to the alps wiki explaining this INITIAL_SITE trick?
Best, Zhenya
On Fri, Jan 23, 2009 at 4:02 PM, Synge Todo wistaria@comp-phys.org wrote: From: Evgeny Burovskiy burovski@alumni.umass.edu Date: Fri, 23 Jan 2009 13:37:22 +0100
Please forgive me for jumping into the discussion: what is the
syntax precisely?
Is this feature implemented in all the applications? I've tried using MEASURE_CORRELATIONS[SzSz,INITIAL_SITE=0]="Sz:Sz" with dmrg, and it gave me same N*(N-1)/2 values.
The syntax is:
MEASURE_CORRELATIONS[SzSz]="Sz:Sz" INITIAL_SITE=0
All the qmc applications should support this feature. But probably dmrg does not.
Synge