[bakpaul]

The philosophy of these new class where to use the same VecID as the current state throughout the integration to prepare the work for the Newton. This mean that the current state (position and velocity) is copied into the working state.

The issue is that after this copy, no propagation was performed. Meaning that for lagrangian-based simulation, the free states where updated with the current state but the mapped states kept the old free state. Leading to the forcefield under those mapping computing the forces values at the freestate of the previous timestep.

This PR fixes this behavior.

Some regression might fail as they might have been wrongly interpreted as non-converged CG because of very little behavior differences.

EDIT:
I have pushed another solution that behave more like the old implementation. This for me is broken mechanically speaking, but first let's bring back the old behavior with stable scenes, then we can rediscuss the ways.

[with-all-tests]

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[fredroy]

I suppose you should adapt the propagation because of

• [Core] Deprecate propagate methods #6312
  and
• [Core,IntegrationScheme] Replace legacy propagation by mapping-graph based propagation #6334

[bakpaul]

Yes it was a quick fix so Eulalie could try it, I'll do it properly. Thx

[fredroy]

Claude detected some problems, one is especially concerning, as it was copying twice the velocity (copy-paste I suppose)
He (it?) also says that AccelerationBasedImplicitIntegrationScheme having the same problem.

[fredroy]

m_vop->v_eq was filtering on the eventual tags apparently, with this->getContext()->executeVisitor the tag filtering is lost. But I dont know it we still really support the tagging system.

[bakpaul]

The tagging system might be important for some diffusion scenes. Tje v_eq was added by me in my IntegrationScheme PR so I didn't make the use of v_eq because of the tag filtering. In other words, if we don't see any changes in the tests, there is no willingness to keep filtering here.

[bakpaul]

That is only half true. I see the copy/paste error, my mistake sorry. Indeed the acceleration-based one suffer the same problem, but this is only an issue when used in a FreeMotionAnimationLoop which is never the case. I'll add it but it will be a bit useless in this case.