[gmx-developers] Wrong Ouput from g_density - PBC bug?

[Juan M. Vanegas]

Actually, I should have run some more tests before posting here, so it 
turns out that there is no issue with the PBC part. The problem is 
actually with the accumulation of the values. Originally the 
accumulation of the densities was done with type "real", but if you have 
gromacs compiled in single precision this array is of type float and you 
get different results depending on the conditions because of the 
precision. Berk Hess changed the type of the variable that accumulates 
the densities explicitly to double sometime in March of 2011

http://repo.or.cz/w/gromacs.git/commit/8c3a82a3caec5dcd04fd11c6f75d2dabbbca86fd 


but then it got changed again to real (by mistake?) a few weeks later, 
and in the latest git version the density storage array is still of type 
real, but needs to be changed to double or you get spurious results.

Juan