AWH covering detection delayed in certain cases - Redmine #2487
Archive from user: Viveca Lindahl
For a Brownian dynamics system with a 2d reaction coordinate, the AWH detection of covering gets delayed because the check frequency is determined to be too high. The check frequency is set to scale with the number of points in the grid but the covering time should not directly depend on the discretization. For Brownian dynamics, the time step can be chosen to be large relative to the diffusion time. This exposed the problem since the number of number of samples needed per covering time is relatively small.
(from redmine: issue id 2487, created on 2018-04-25 by gmxdefault, closed on 2018-06-14)
- Revision 26db2acf on 2018-06-12T10:02:13Z:
Changed histogram check interval for multidimensional AWH bias.
The step interval for performing covering checks depended explicitly
on the total number of points in the AWH histogram. The covering
checks themselves however only depends directly on the extent of each
one-dimensional axis. For a multidimensional grid in combination with
relatively few samples to cover the sampling interval (e.g. using
Brownian dynamics), this could lead to a delayed detection of the
The same step interval was also used for checking for histogram
anomalies, which however only generates warnings and is not integral
to the AWH method itself.
Now the covering check interval is instead determined from the number
of sigmas, the "width" of one sample, required to cover each
dimension. Since there is about 1 point per sigma, the dependency of
the check interval on the number of points is essentially unchanged in
the one-dimensional case. However, this relation is not numerically
exact. Therefore, this change also requires updating reference data
for a regression test to be updated.
The check interval for histogram anomalies is set to be the same as
for the covering, but could in the future be made less frequent.
Added release note.