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[Václav Šmilauer <eudoxos@xxxxxxxx>]

> what the hell continuum mechanics as to do with interactions in multibody systems?
They happen to be computed by the same program of which I happen to be the main dev currently. Voting about such things is really a bad idea.

Branch contact+geomechanics yade version where you make everything the
inverse, if you like; if not, we need to keep one background for
everything, and there continuum mechanics is what seems more established
to me.

You can add ass well an alternative #3, that interaction is "from 2 to
1"...

-- 
NormalShearInteraction::{normalForce,shearForce} has undefined orientation
https://bugs.launchpad.net/bugs/493102
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Status in Yet Another Dynamic Engine: Confirmed

Bug description:
NormalShearInteraction::{normalForce,shearForce} should contain forces on the interaction, which can be used for various purposes by other functions. However, different functors use them with different sign

ef2_Spheres_Elastic_ElasticLaw (a.k.a. ElasticContactLaw):

   applyForceAtContactPoint(-currentContactPhysics->normalForce-shearForce, ... )

Law2_Dem3DofGeom_CpmPhys_Cpm:

   applyForceAtContactPoint(BC->normalForce+BC->shearForce, ...)

This is a convention issue, but must be fixed. Should normalForce and shearForce be oriented as it applies on id1 (first case) or id2 (second case)? 2nd case is nicer WRT applyForceAtContactPoint syntax, but that one is arbitrary as well.