Hi @alxbilger,

Thanks for the PR.
It looks really nice to me, when looking at it I'm wondering wether or not there is possible memory pointer issues... I mean if the object is removed from the scene graph is it possible that dangling pointer remains on the python side ?

I don't think so. The returned object of those bindings are copies in all functions A, b and x. For A, there is no choice as pybind cannot pass a sparse matrix by reference (Passing by reference is not supported for sparse types.). b and x return also a copy, but here they are dense vectors, so in theory there is room for improvement to pass the vectors by reference.

A unit test is required

Thanks for the added tests @alxbilger.

To make python scenes it is recommended to use python objects instead of Sofa string for passing parameters.

root.addObject('EulerImplicitSolver', rayleighStiffness="0.1", rayleighMass="0.1") 
root.addObject('BoxROI', name="box", box="-10 -1 -0.0001 -5 4 0.0001")

should become:

root.addObject('EulerImplicitSolver', rayleighStiffness=0.1, rayleighMass=0.1) 
root.addObject('BoxROI', name="box", box=[-10, -1, -0.0001, -5, 4, 0.0001])

@damienmarchal thanks for the review. The last changes should follow your suggestions

I suspect the failing unit test comes from sofa-framework/sofa#3036, highlighted by sofa-framework/sofa#3050.
Therefore, I'll modify the test

The generated file BindingsConfig.cmake does not work when used in find_package for an external directory. There is a failure on missing Bindings.SofaBaseLinearSolver.