ickby wrote: ↑Thu Oct 31, 2019 7:01 am
Back then when I tried to write a 3d solver for assemblies I failed for that very reason: standard numeric solvers are unable to cope with the fact that rotational and transitional degrees of freedom have different sensitivities, a unit change in the parameter leads to to massively different changes in the sketch dependent on the type of parameter. So the sensitivity for translation to translation is always 1, angle to angle also always 1, but angle to translation may be way higher. That is a unsolvable problem, as reducing the angle sensitivities may solve angle to translation problem, but than created a angle to angle sensitivity problem, as this gets way too small or big dependet on scaling. Another issue is that one solver variable is part of many output dofs, hence you would need different scaling for each single output dof but have only one scaling factor for the variable.

Thank you for this post. All these problems i can confirm and found them during development of my 3D solver within the A2plus WB. As the solver of A2plus is not a standard numeric solver and each constraint is coded separatly, often the boundbox size of a part is taken into calculation, to avoid scaling dimensions effects. But i still have numerical stability issues, especially on long dof chains.

I think similar effects may affect the 2D sketch solver.