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