Dear Mr Troyer,<br><br>I&#39;m using ALPS to run MC simulations of classical Ising, XY and Heisenberg models in three dimensions. I want to study how the critical values of some observables varies with L in a regular cubic lattice so I run the simulations at T_c (critical value of the temperature).<br>
<br>I know that at the phase transition you have strong correlation in the system and it is difficult to obtain values of the observables with convergence on the errors. For this reasons I have the following questions:<br>
<br>1) Errors on the observables are given with three different levels of &#39;accuracy&#39;: converged (white), check the convergence (yellow), not converged (red). <br>How does the program test if the convergence is achieved? I mean I see the program evaluate the errors dividing the total number of steps in groups of binning and then evaluating the errors group by group. I suppose that it says that the convergence is achieved if the errors in different groups vary less then some interval that is fixed...is it true? Which is the test that it does?<br>
<br>2) I suppose Tau is the correlation time. Does the program take into account the value of Tau in the final valuation of the errors? I mean, are those errors already multiplied by the sqrt of tau as it must be in case of correlations, or must be corrected bye the value of tau that is given?<br>
<br>3) Since the correlation is strong at T_c do you think that it could be easier to get to convergence if we change the initial configuration of the MC? For example we could run a simulation for a while then take the last configuration it uses to evaluate the values of observables and then use this last configuration as the input configuration for a new run...can it be done in some way?<br>
<br>4) Some months ago I wrote to you to ask if it could be possible to run a classical MC simulation for an O(4) model. in the tutorials you say that it can be done simply editing the spin_factory.C file. I tried but still it doesn&#39;t work. I&#39;m afraid I made some mistakes in the installation of the ALPS library on my PC. Did you add this option in the new version 2.0?<br>
<br>Thank you very much for the help and I&#39;m sorry to bother you with all these questions.<br><br>I wish you my best regards <br><br>Rachele Nerattini<br><br>  <br>