Dear All,
I have a question about the ALPS implementation of the Worm algorithm. In
every paper I read about the Worm algorithm the same idea pervades: the
Worm algorithm can easily sample Green's function(in imaginary time)
because the movements of the worm do precisely that. Or in other words,
Green's functions can be measured by histogramming the relative position of
the head and tail of the worm(adding a 1 to the G(i-j,tau2-tau1) entry
whenever the head is at i,tau2 and the tail is at j,tau1).
The current version of the ALPS Worm code(alps 2.1) does not measure
Green's functions and the issue was discussed, albeit briefly, earlier this
year in a couple of e-mails, and it was mentioned that it would actually be
too costly computationally to get all the N^2 values and only the relative
distances would be measured. Is it because of the computational time needed
in the Green's function configuration space would be too long and the
current implementation samples mostly the partition function configuration
space(by shifting/moving closed loops)? Or is it due to some technical
detail that is usually not mentioned in the papers?(or that I might have
not understood it correctly).
Cheers,
Francisco Cordobes