[gmx-developers] stuff in double precision

[Erik Lindahl]

Hi,

On Feb 5, 2007, at 7:35 PM, David Mobley wrote:

>
> The reason free energy calculations (absolute or relative) work (or
> are supposed to work) isn't that they avoid subtracting large numbers
> -- it's that they evaluate the potential energy of a particular
> snapshot in different Hamiltonians (or, similarly, the free energy
> derivative for a particular snapshot).

Agreed, and of course we should get it to work that way. Using double  
is a bad solution, simply because it's just pushing the problem  
towards larger systems (OK, pretty large ones :-), but since some  
tabulated interactions don't quite have full double precision it is  
probably wiser to address the problem (e.g. summation order) rather  
than just using double to hide it.

Cheers,

Erik