[gmx-developers] single precision, double precision hybrid GROMACS

[Berk Hess]

First I must say that I agree completely with Mark.

But I have tried doing the constraints only in double precision.
Thus x is float, but xprime is double and all constraints algorithms 
double precision.
This did not improve the accuracy.
It might be that one could improve things by also making x double precision.
I would assume that you need to have the position increment very accurate
to have accurate compensation of potential and constraints forces.
But that was to much effort for me, as then x would have to be double
precision throughtout the whole code, except in the innerloop calls,
which would also make it questionable if it would really improve things.

Making x double precision in the innerloops in not a viable option,
since then you could not uses the assembly loops
and then assembly full double precision is anyhow faster.

Berk.