[binding] QPInverseProblemSolver: adds python binding

[EulalieCoevoet]

Usage example:

import Sofa.SoftRobotsInverse

class MyQPInverseProblemSolver(Sofa.SoftRobotsInverse.QPInverseProblemSolver):

    def __init__(self, *args, **kwargs):
        Sofa.SoftRobotsInverse.QPInverseProblemSolver.__init__(self, *args, **kwargs)

    def solveSystem(self):
        W = self.W()
        dfree = self.dfree()
        forces = self.lambda_force()  # pointer on lambda
        [...] # solve the problem and store the result in forces
        return True

def createScene(rootnode):
    rootnode.addObject(MyQPInverseProblemSolver)
    [...]

[damienmarchal]

I gave it a quick look and seems ok.

[alxbilger]

I wonder why you need this whereas there is already these bindings for ConstraintSolverImpl.

[EulalieCoevoet]

I thought the same, but I didn't find why it does not work.

[damienmarchal]

Can you elaborate a bit ? What is not working ?

[EulalieCoevoet]

When used like that:

import Sofa.SoftRobotsInverse
import Sofa.SofaConstraintSolver


class MyQPInverseProblemSolver(Sofa.SoftRobotsInverse.QPInverseProblemSolver):

    def __init__(self, emio, *args, **kwargs):
        Sofa.SoftRobotsInverse.QPInverseProblemSolver.__init__(self, *args, **kwargs)

    def solveSystem(self):
        W = self.W()
        dfree = self.dfree()
        torques = self.lambda_force()
        return True

The calls to W(), dfree(), and lambda_force() do not work, meaning I get :

terminate called after throwing an instance of 'pybind11::error_already_set'
what():  AttributeError: Unable to find attribute: W

[damienmarchal]

This is not the expected behavior :)

What is the result of:

q =  MyQPInverseProblemSolver(name="q")
print(dir(q))      # What is the content of q
print(type(q))   # And its type

# Adding the python object 'q' to c++ sofa... 
root.addObject(q)
  
# And retrieve it from the rootNode (so converting it back to python)
q = rootNode.q                
print(dir(q))      # What is the content of q
print(type(q))   # And its type

[EulalieCoevoet]

['actuatorsOnly', 'allowSliding', 'bbox', 'componentState', 'countdown', 'displayTime', 'epsilon', 'info', 'listening', 'maxContactForces', 'maxIterations', 'minContactForces', 'multithreading', 'name', 'objective', 'printLog', 'responseFriction', 'reverseAccumulateOrder', 'saveMatrices', 'tags', 'tolerance']
<class 'lab2-inversekinematics.MyQPInverseProblemSolver'>
['actuatorsOnly', 'allowSliding', 'bbox', 'componentState', 'countdown', 'displayTime', 'epsilon', 'info', 'listening', 'maxContactForces', 'maxIterations', 'minContactForces', 'multithreading', 'name', 'objective', 'printLog', 'responseFriction', 'reverseAccumulateOrder', 'saveMatrices', 'tags', 'tolerance']
<class 'lab2-inversekinematics.MyQPInverseProblemSolver'>

[alxbilger]

The unit test https://github.com/alxbilger/SofaPython3/blob/d16750f7fa6fe1075876877fc831f4d225ec9f90/bindings/Modules/tests/SofaConstraintSolver/matrix_access.py works for me with the following changes (without your PR):

                                                      "Sofa.Component.Mapping.MappedMatrix",
                                                      "Sofa.Component.Mass",
                                                      "Sofa.Component.ODESolver.Backward",
-                                                     "Sofa.Component.Topology.Container.Dynamic"])
+                                                     "Sofa.Component.Topology.Container.Dynamic",
+                                                     "SoftRobots.Inverse"])
 
         root.addObject("FreeMotionAnimationLoop", solveVelocityConstraintFirst=True)
-        root.addObject("GenericConstraintSolver", name="constraint_solver", tolerance=1e-9, maxIterations=1000)
+        root.addObject("QPInverseProblemSolver", name="constraint_solver", tolerance=1e-9, maxIterations=1000)
         root.addObject("StringMeshCreator", name="loader", resolution="20")
 
         root.addObject("EulerImplicitSolver")

Could you check that you have the same result?

[EulalieCoevoet]

The unit test https://github.com/alxbilger/SofaPython3/blob/d16750f7fa6fe1075876877fc831f4d225ec9f90/bindings/Modules/tests/SofaConstraintSolver/matrix_access.py works for me with the following changes (without your PR).
Could you check that you have the same result?

Yes it works. What does not work is when used like that (without duplicating what you did in the module SofaConstraintSolver):

import Sofa.SoftRobotsInverse
import Sofa.SofaConstraintSolver


class MyQPInverseProblemSolver(Sofa.SoftRobotsInverse.QPInverseProblemSolver):

    def __init__(self, emio, *args, **kwargs):
        Sofa.SoftRobotsInverse.QPInverseProblemSolver.__init__(self, *args, **kwargs)

    def solveSystem(self):
        W = self.W()
        dfree = self.dfree()
        torques = self.lambda_force()
        return True

[alxbilger]

I am considering adding a trampoline class for ConstraintSolverImpl, not only for QPInverseProblemSolver. I see that your version needs specific data from QPInverseProblemSolver in storeResults. Would it be required to write its own storeResults for ConstraintSolverImpl?