[gmx-developers] Extracting i-j forces from nb_generic.c

[Mark Abraham]

Yeah, that's what I meant. Multiply thing by -1 or take some other thing to
the power -1, it's all the same right? :-P

Mark


On Sun, Feb 2, 2014 at 8:51 PM, Erik Lindahl <erik.lindahl at scilifelab.se>wrote:

> Hi,
>
> On 02 Feb 2014, at 20:11, Mark Abraham <mark.j.abraham at gmail.com> wrote:
> >
> > Do take care - components of fscal are not actually the scalar force,
> but the negative of it (because mostly it saves a flop).
>
> For the record, it can be even worse than this. In many (most) places we
> need to multply the force with the interparticle vector to get the
> vectorial force. However, it would be expensive (and stupid) computationall
> to normalize this vector when we already have 1/r available. Thus, fscal is
> often the scalar force *divided by r*, so we can then multiply it by the
> non-normalized interparticle vector.
>
> Cheers,
>
> Erik
>
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