[gmx-developers] stuff in double precision

Erik Lindahl lindahl at cbr.su.se
Mon Feb 5 19:52:19 CET 2007


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.



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