[SOLVED] What is the mechanism of BilateralInteractionConstraint?

[Wong]

Hello everyone,

I wanted to know more about the mechanism and the theory of the constraint component but later I found the code so hard to comprehend.

Then I noticed the post https://www.sofa-framework.org/community/forum/topic/how-to-create-bilateral-constraint/ . Eventually, I understood a part of the component BilateralInteractionConstraint. Three functions are important: buildConstraintMatrix, getConstraintViolation and getConstraintResolution.

But currently, I still cannot really understand some content of the BilateralInteractionConstraint.

The function buildConstraintMatrix has two parameters:DataMatrixDeriv &c1_d, DataMatrixDeriv &c2_d. What is the specific form(or data structure) of the type DataMatrixDeriv? I think the method c1_it.addCol must be use in to add constraints in function buildConstraintMatrix.But its utility is flexible:

MatrixDerivRowIterator c2_it = c2.writeLine(cid[pid]);
c2_it.addCol(tm2, cx); (in BilateralInteractionConstraint.inl)

MatrixDerivRowIterator c2_it = c2.writeLine(cid[pid]);
c2_it.addCol(tm2, Deriv(cx, vZero)); (in BilateralInteractionConstraint.cpp)

MatrixDerivRowIterator c2_it = c2.writeLine(cid);
c2_it.addCol(tm2a, -dir1 * (1-r2));
c2_it.addCol(tm2b, -dir1 * r2); (in SlidingConstraint.inl)

And I do not konw the type DataMatrixDeriv and DataMatrixDeriv.

Likewise,in getConstraintResolution, BilateralConstraintResolution is flexible:

resTab[offset] = new BilateralConstraintResolution3Dof(&prevForces[pid]);(in BilateralInteractionConstraint.inl)

resTab[offset] = new BilateralConstraintResolution3Dof();(in BilateralInteractionConstraint.cpp)

resTab[offset++] = new BilateralConstraintResolution();(in SlidingConstraint.inl)

And I also cannot understand the parameter &prevForces[pid].

Maybe it is just because I do not know the solving process of the constraint. So I want to understand the theory of the constraint solvers.

For instance, what is the meaning of the equation trans(H).A.H λ = trans(H).y – d ?(at https://www.sofa-framework.org/community/forum/topic/how-to-create-bilateral-constraint/)

And the code about solving process is not in the constraint component. Need I read the code of the GenericConstraintSolver?

What kind of reference can I find some content about constraint or constraint solver in?

Any help and hits are appreciated.

Wong

[Hugo]

Dear @outtt

This thread is very old and a doc page is now available.
I close it.
Open a new one if you have further issue.

Hugo

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