UPPER_WALLS or LOWER_WALLS and PBCs

[GiovanniBussi]

It looks like applying PBCs on the difference between the current CV value and that of the wall might not be the correct thing to do. See this post for a practical example.

Should we just replace:

const double cv=difference(i,at[i],getArgument(i));

with

const double cv=getArgument(i)-at[i];

?

I am not totally sure this is the right thing to do. Maybe adding a NOPBC flag to UPPER_WALLS and LOWER_WALLS to disable PBC?

[carlocamilloni]

I think that the point is that a single upper/lower wall on a periodic CV is meaningless, anyway for u/l walls possible the correct thing is to calculate the distance as cv=getArgument(i)-at[I]; but also throw an error if the CV is periodic (in case suggesting to remove the periodicity using COMBINE)

[Clownshift]

Hi Devs, I am trying to use the upper and lower walls bias modules. I wonder if there is any news about this potential issue...?