**From:** Jérôme Hénin (*jerome.henin_at_ibpc.fr*)

**Date:** Wed Mar 13 2019 - 09:37:31 CDT

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Dear Haochuan,

Yes. That is handled at the atom group level by enableFitGradients, which

defaults to true. Cases where the calculation is not supported will trigger

a dependency failure, so you cannot miss them.

Best,

Jérôme

On Wed, 13 Mar 2019 at 14:04, <yjcoshc_at_gmail.com> wrote:

*> Dear NAMD and Colvars developers,
*

*>
*

*> If I have a vector *v* = *R* * *X* - *X*_ref, where the *X* is current
*

*> Cartesian coordinates of a set of atoms, *X*_ref is the reference
*

*> coordinates and *R* is the optimal rotation matrix, and in the C++
*

*> interface I have correctly setup the ref_pos of atom_group *X* in the C++
*

*> interface. Assuming I have a scalar function f(*v*) and I know the
*

*> derivative of f with respect of *v* (df/d*v*), can I use df/d*v *as the
*

*> atomic gradients of atom_group *X*? In other words, can I assume d*R*/d*X*
*

*> is automatically computed when I have setup b_rotate and ref_pos of *X*
*

*> in the atom_group initialization?
*

*>
*

*> Thanks,
*

*>
*

*> Haochuan Chen
*

*>
*

*>
*

*>
*

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