Hi Professor Todo,

Sorry to bother you again. But what if I want to measure <M_x^2>=<\cos^2\theta> or the nematic <N_x>=<\cos 2\theta> of XY model by ALPS? I have googled it but didn't find anything related. Could you kindly give me some suggestions? Or I need to modify the source code of ALPS to achieve it?

Looking forward to your reply!

Regards,

Wei

On Sep 30, 2020, at 10:29, Synge Todo <wistaria@phys.s.u-tokyo.ac.jp> wrote:

Dear Wei,

Indeed, <\cos\theta> is zero if there is no external magnetic field.
If there is a non-zero magnetic field, 'Magnetization along Field' is the quantity you are looking for.

Best,
Synge

On Sep 30, 2020, at 11:03, Wei Wang <wei.wang@jhu.edu> wrote:

Dear Prof. Todo,

Thank you for your reply! I have added these two lines into my code, and print the measurements out:

set(['Magnetization^2', 'Binder Cumulant', 'Specific Heat', '|Magnetization|', 'Magnetization^4', '|Staggered Magnetization|', 'Staggered Magnetization^2', 'E.Magnetization^4’, 
'E.Magnetization^2', 'Energy Density', 'Susceptibility', 'beta * Energy / sqrt(N)', 'Magnetization along Field', 'Magnetization^4 slope', 'Connected Susceptibility', 'Magnetization^2
slope', 'Binder Cumulant U2', 'Cluster size', 'Bond-type Energy', 'Energy', 'Bond-type Energy Density', 'Energy^2', '(beta * Energy)^2 / N', 'Binder Cumulant slope'])

I don’t find an observable like the <\cos\theta>, or which of the measurements above can give me the directions of the magnetization. Please forgive me if this is a silly question, I am a 1st-year graduate student learning how to use ALPS. Thank you!

Regards,
Wei

On Sep 30, 2020, at 09:45, Synge Todo <wistaria@phys.s.u-tokyo.ac.jp> wrote:

Dear Wei,

You can obtain a list of measurements by

data = pyalps.loadMeasurements(pyalps.getResultFiles(prefix='data/parmXY'))
measurements = { item.props['observable'] for item in pyalps.flatten(data) }

Best,
Synge

On Sep 30, 2020, at 9:49, Wei Wang <wei.wang@jhu.edu> wrote:

Hi,

I am just new to ALPS, and I have a silly question about running MC simulations of XY model:

Following the tutorials, I use python to run the simulations and change the model from “Ising” to “XY”, like:

import pyalps

parms = [
  {
      'LATTICE': "square lattice",
      'T': 1,
      'J': 1,
      'THERMALIZATION': 10000,
      'SWEEPS': 400000,
      'UPDATE': "cluster",
      'MODEL': "XY",
      'L': 8
  }
]

input_file = pyalps.writeInputFiles('data/parmXY', parms)
pyalps.runApplication('spinmc', input_file, Tmin=5)
result_files = pyalps.getResultFiles(prefix='data/parmXY')

data = pyalps.loadMeasurements(result_files)

how can I get some observables like <\cos\theta>, where \theta is the direction of the spin at each site? If such a quantity is not provided directly by ALPS, is there a possible method to get these quantities I want. I just get lost when I see the source code of ALPS.

Thank you in advance!

Best,
Wei



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