|From:||Joost de Graaf|
|Subject:||Re: [ESPResSo-users] Force scaling wrong|
|Date:||Sun, 1 Mar 2015 11:29:39 +0100|
just a brief comment:
My interpretation to the "force settable" question so far was:
Why would we need settable forces, if we have settable ext_forces? I can only think of prototyping situations, but not production situations where the actual forces have to be settable.
On Feb 28, 2015, at 6:06 PM, Ulf Schiller <address@hidden> wrote:
> On 02/28/2015 12:09 PM, Joost de Graaf wrote:
>> Dear Floh & Marcello,
>> I'm not sure if it's that good an idea to make the forces read-only. I
>> can assure you, they are definitely not that way in the current code and
>> for good reasons. If you want to reinitialize the LB fluid, you need the
>> reuse_forces command, to account for the fact that the LB use of forces
>> is half a time step off of that in the main integration loop. That's why
>> you want to keep them settable. (as I wrote this Henri's message came in).
> This is only needed if you desire exactly reproducible trajectories
> (which of course is helpful for debugging). The sampling would still be
> valid (and actually more accurate) if one just recalculates the forces
> (adjusting the noise amplitude appropriately). That is basically just
> another instance where velocity dependent forces reduce the accuracy of
> ESPResSo's integrator by an order anyways, same for the LB update.
>> On 28 February 2015 at 12:23, Florian Weik <address@hidden
>> <mailto:address@hidden>> wrote:
>> Marcello is right, these forces are never used. For technical
>> reasons it is not that easy to make them read-only because a lot of
>> the test cases rely on the fact that forces can be read via the
>> blockfile mechanism which is in turn just an interface to the tcl
>> part command. So unless somebody is volunteering for the busywork to
>> change dozens of test cases, that situation is staying the way it
>> is. I'm pretty sure the documentation reflects the fact that these
>> forces are not used.
>> On Sat, Feb 28, 2015 at 8:36 AM, Marcello Sega
>> <address@hidden <mailto:address@hidden>> wrote:
>> please correct me if I'm wrong: I think that forces are always
>> overwritten by the integrator, so that setting them by hand does not
>> have any effect at all.
>> If this is right, then allowing to set forces could be just
>> (as the program would behave in a way unexpected by the user).
>> Wouldn't it be better to make them read-only?
>> On Fri, Feb 27, 2015 at 3:56 PM, Henri Menke
>> <address@hidden <mailto:address@hidden>>
>>> Dear all,
>>> in the current master of ESPResSo the forces are scaled by the
>>> and the time step in the output, i.e. part 0 print f, but are
>> not scaled
>>> by the mass in the input, i.e. part 0 f. This leads to wrong
>>> when setting them by hand with a mass not equal to 1.
>>> This bug is fixed in the pull-request
>>> Kind regards,
>> Institut für Computergestützte Biologische Chemie
>> University of Vienna
>> PGP public key on MIT server http://goo.gl/zlIZix
>> Florian Weik, Dipl.-Phys.,
>> Institut für Computerphysik, Allmandring 3, D-70569 Stuttgart
>> Phone: +49-711-685-67703 <tel:%2B49-711-685-67703>
>> Public Key 0x0562F11D Fingerprint 3294 6360 EC93 37A3 BD40 F597
>> 0BAD 3AF8 0562 F11D
> Ulf D. Schiller
> Centre for Computational Science
> University College London
> 20 Gordon Street
> London WC1H 0AJ
> United Kingdom
> Phone: +44 (0)20 7679 5300
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