On 2 Sep 2008, at 16:10, João Manuel Viana Parente Lopes wrote:

Dear Matthias Troyer and Synge Todo,

I'm sorry for the late response but I was away from my computer several days! Thank's for your help!!

I increased the number of SWEEPS and I have finally found the square root behaviour of the error bars as a function of the number of SWEEPS. I imagine (I didn't had time to check yet) the method of estimation of the error bars makes an underestimation of the variance.

Don't assume that it just makes the number of sweeps you ask, but check the count of measurements, and use that in your comparison. For tiny systems even if you ask for few sweeps it might do many more.

And yes, if you run it for far too short times the variance is underestimated. You need to run at least a few autocorrelation times.

Matthias