[gmx-developers] Use of invsqrt with tables

[Berk Hess]

Hi,

But avoiding the inversion is not possible, since you need to multiply 
the scaling force by the normalized distance vector.

Berk

On 2016-03-23 13:00, David van der Spoel wrote:
> Hi,
>
> In all versions of gromacs the distance between two nonbonded atoms is 
> computed as
>             rinv00           = gmx_invsqrt(rsq00);
>             r00              = rsq00*rinv00;
>
> This is fine when we use Lennard Jones and Coulomb, but not when using 
> table potentials which do not necessarily have singularities at r = 0. 
> I would therefore propose to replace the statements by a normal sqrt 
> in all innerloops using tables.
>
> Thoughts?