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