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[FEM.Elastic] Remove complex unproductive stiffness matrix data structure #6133

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6ee6d7d
[FEM.Elastic] Remove complex unproductive stiffness matrix data struc…
alxbilger May 28, 2026
38ca0d1
rename ElementForce to ElementGradient
alxbilger May 28, 2026
52c475c
explicit namespace
alxbilger May 29, 2026
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4 changes: 2 additions & 2 deletions ...EM/Elastic/src/sofa/component/solidmechanics/fem/elastic/BaseElementLinearFEMForceField.h
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Expand Up @@ -51,7 +51,7 @@ class BaseElementLinearFEMForceField : public sofa::component::solidmechanics::f

private:
using trait = sofa::component::solidmechanics::fem::elastic::trait<DataTypes, ElementType>;
using ElementStiffness = typename trait::ElementStiffness;
using ElementHessian = typename trait::ElementHessian;
using StrainDisplacement = typename trait::StrainDisplacement;
using Real = typename trait::Real;

Expand All @@ -69,7 +69,7 @@ class BaseElementLinearFEMForceField : public sofa::component::solidmechanics::f
/**
* List of precomputed element stiffness matrices
*/
sofa::Data<sofa::type::vector<ElementStiffness> > d_elementStiffness;
sofa::Data<sofa::type::vector<ElementHessian> > d_elementStiffness;
};

#if !defined(ELASTICITY_COMPONENT_BASE_ELEMENT_LINEAR_FEM_FORCEFIELD_CPP)
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3 changes: 2 additions & 1 deletion .../Elastic/src/sofa/component/solidmechanics/fem/elastic/BaseElementLinearFEMForceField.inl
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Expand Up @@ -23,6 +23,7 @@

#include <sofa/component/solidmechanics/fem/elastic/BaseElementLinearFEMForceField.h>
#include <sofa/component/solidmechanics/fem/elastic/BaseLinearElasticityFEMForceField.inl>
#include <sofa/component/solidmechanics/fem/elastic/impl/ElementStiffnessMatrix.h>
#include <sofa/component/solidmechanics/fem/elastic/impl/LameParameters.h>
#include <sofa/component/solidmechanics/fem/elastic/impl/VectorTools.h>

Expand Down Expand Up @@ -98,7 +99,7 @@ void BaseElementLinearFEMForceField<DataTypes, ElementType>::precomputeElementSt
const auto elasticityTensor = makeIsotropicElasticityTensor<DataTypes::spatial_dimensions, Real>(mu, lambda);

const std::array<sofa::Coord_t<DataTypes>, trait::NumberOfNodesInElement> nodesCoordinates = extractNodesVectorFromGlobalVector(element, restPositionAccessor.ref());
elementStiffness[elementId] = integrate<DataTypes, ElementType, trait::matrixVectorProductType>(nodesCoordinates, elasticityTensor);
elementStiffness[elementId] = integrate<DataTypes, ElementType>(nodesCoordinates, elasticityTensor);
});
}

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8 changes: 4 additions & 4 deletions .../Elastic/src/sofa/component/solidmechanics/fem/elastic/ElementCorotationalFEMForceField.h
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Expand Up @@ -138,7 +138,7 @@ class ElementCorotationalFEMForceField :

private:
using trait = sofa::component::solidmechanics::fem::elastic::trait<DataTypes, ElementType>;
using ElementForce = typename trait::ElementForce;
using ElementGradient = typename trait::ElementGradient;
using RotationMatrix = sofa::type::Mat<trait::spatial_dimensions, trait::spatial_dimensions, sofa::Real_t<DataTypes>>;


Expand All @@ -158,19 +158,19 @@ class ElementCorotationalFEMForceField :
protected:

void beforeElementForce(const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& f,
sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x) override;

void computeElementsForces(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& f,
sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x) override;

void computeElementsForcesDeriv(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForcesDeriv,
sofa::type::vector<ElementGradient>& elementForcesDeriv,
const sofa::VecDeriv_t<DataTypes>& nodeDx) override;

sofa::type::vector<RotationMatrix> m_rotations;
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8 changes: 4 additions & 4 deletions ...lastic/src/sofa/component/solidmechanics/fem/elastic/ElementCorotationalFEMForceField.inl
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Expand Up @@ -72,7 +72,7 @@ void ElementCorotationalFEMForceField<DataTypes, ElementType>::init()

template <class DataTypes, class ElementType>
void ElementCorotationalFEMForceField<DataTypes, ElementType>::beforeElementForce(
const sofa::core::MechanicalParams* mparams, sofa::type::vector<ElementForce>& f,
const sofa::core::MechanicalParams* mparams, sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x)
{
const auto& elements = trait::FiniteElement::getElementSequence(*this->l_topology);
Expand All @@ -82,7 +82,7 @@ void ElementCorotationalFEMForceField<DataTypes, ElementType>::beforeElementForc
template <class DataTypes, class ElementType>
void ElementCorotationalFEMForceField<DataTypes, ElementType>::computeElementsForces(
const sofa::simulation::Range<std::size_t>& range, const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForces, const sofa::VecCoord_t<DataTypes>& nodePositions)
sofa::type::vector<ElementGradient>& elementForces, const sofa::VecCoord_t<DataTypes>& nodePositions)
{
const auto& elements = trait::FiniteElement::getElementSequence(*this->l_topology);
auto restPositionAccessor = this->mstate->readRestPositions();
Expand Down Expand Up @@ -130,7 +130,7 @@ template <class DataTypes, class ElementType>
void ElementCorotationalFEMForceField<DataTypes, ElementType>::computeElementsForcesDeriv(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForcesDeriv,
sofa::type::vector<ElementGradient>& elementForcesDeriv,
const sofa::VecDeriv_t<DataTypes>& nodeDx)
{
const auto& elements = trait::FiniteElement::getElementSequence(*this->l_topology);
Expand Down Expand Up @@ -193,7 +193,7 @@ void ElementCorotationalFEMForceField<DataTypes, ElementType>::buildStiffnessMat
{
for (sofa::Index n2 = 0; n2 < trait::NumberOfNodesInElement; ++n2)
{
stiffnessMatrix.getAssembledMatrix().getsub(trait::spatial_dimensions * n1, trait::spatial_dimensions * n2, localMatrix); // extract the submatrix corresponding to the coupling of nodes n1 and n2
stiffnessMatrix.getsub(trait::spatial_dimensions * n1, trait::spatial_dimensions * n2, localMatrix); // extract the submatrix corresponding to the coupling of nodes n1 and n2
dfdx(element[n1] * trait::spatial_dimensions, element[n2] * trait::spatial_dimensions) += -elementRotation * localMatrix * elementRotation_T;
}
}
Expand Down
8 changes: 4 additions & 4 deletions ...tic/src/sofa/component/solidmechanics/fem/elastic/ElementLinearSmallStrainFEMForceField.h
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Expand Up @@ -62,10 +62,10 @@ class ElementLinearSmallStrainFEMForceField :

private:
using trait = sofa::component::solidmechanics::fem::elastic::trait<DataTypes, ElementType>;
using ElementStiffness = typename trait::ElementStiffness;
using ElementHessian = typename trait::ElementHessian;
using ElementDisplacement = typename trait::ElementDisplacement;
using StrainDisplacement = typename trait::StrainDisplacement;
using ElementForce = typename trait::ElementForce;
using ElementGradient = typename trait::ElementGradient;

public:
void init() override;
Expand All @@ -84,13 +84,13 @@ class ElementLinearSmallStrainFEMForceField :
void computeElementsForces(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForces,
sofa::type::vector<ElementGradient>& elementForces,
const sofa::VecCoord_t<DataTypes>& nodePositions) override;

void computeElementsForcesDeriv(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForcesDeriv,
sofa::type::vector<ElementGradient>& elementForcesDeriv,
const sofa::VecDeriv_t<DataTypes>& nodeDx) override;

};
Expand Down
8 changes: 4 additions & 4 deletions ...c/src/sofa/component/solidmechanics/fem/elastic/ElementLinearSmallStrainFEMForceField.inl
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Expand Up @@ -44,7 +44,7 @@ template <class DataTypes, class ElementType>
void ElementLinearSmallStrainFEMForceField<DataTypes, ElementType>::computeElementsForces(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForces,
sofa::type::vector<ElementGradient>& elementForces,
const sofa::VecCoord_t<DataTypes>& nodePositions)
{
const auto& elements = trait::FiniteElement::getElementSequence(*this->l_topology);
Expand Down Expand Up @@ -75,7 +75,7 @@ template <class DataTypes, class ElementType>
void ElementLinearSmallStrainFEMForceField<DataTypes, ElementType>::computeElementsForcesDeriv(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& elementForcesDeriv,
sofa::type::vector<ElementGradient>& elementForcesDeriv,
const sofa::VecDeriv_t<DataTypes>& nodeDx)
{
const auto& elements = trait::FiniteElement::getElementSequence(*this->l_topology);
Expand Down Expand Up @@ -133,7 +133,7 @@ void ElementLinearSmallStrainFEMForceField<DataTypes, ElementType>::buildStiffne
{
for (sofa::Index n2 = 0; n2 < trait::NumberOfNodesInElement; ++n2)
{
stiffnessMatrix.getAssembledMatrix().getsub(trait::spatial_dimensions * n1, trait::spatial_dimensions * n2, localMatrix); //extract the submatrix corresponding to the coupling of nodes n1 and n2
stiffnessMatrix.getsub(trait::spatial_dimensions * n1, trait::spatial_dimensions * n2, localMatrix); //extract the submatrix corresponding to the coupling of nodes n1 and n2
dfdx(element[n1] * trait::spatial_dimensions, element[n2] * trait::spatial_dimensions) += -localMatrix;
}
}
Expand Down Expand Up @@ -169,7 +169,7 @@ void ElementLinearSmallStrainFEMForceField<DataTypes, ElementType>::addKToMatrix
{
for (sofa::Index n2 = 0; n2 < trait::NumberOfNodesInElement; ++n2)
{
stiffnessMatrix.getAssembledMatrix().getsub(trait::spatial_dimensions * n1, trait::spatial_dimensions * n2, localMatrix); //extract the submatrix corresponding to the coupling of nodes n1 and n2
stiffnessMatrix.getsub(trait::spatial_dimensions * n1, trait::spatial_dimensions * n2, localMatrix); //extract the submatrix corresponding to the coupling of nodes n1 and n2

const auto value = (-static_cast<sofa::Real_t<DataTypes>>(kFact)) * static_cast<sofa::type::ScalarOrMatrix<LocalMatType>>(localMatrix);
matrix->add(
Expand Down
12 changes: 6 additions & 6 deletions .../SolidMechanics/FEM/Elastic/src/sofa/component/solidmechanics/fem/elastic/FEMForceField.h
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Expand Up @@ -50,7 +50,7 @@ class FEMForceField :

private:
using trait = sofa::component::solidmechanics::fem::elastic::trait<DataTypes, ElementType>;
using ElementForce = typename trait::ElementForce;
using ElementGradient = typename trait::ElementGradient;

public:
void init() override;
Expand Down Expand Up @@ -81,17 +81,17 @@ class FEMForceField :
/// Methods related to addForce
/// @{
void computeElementsForces(const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& f,
sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x);

virtual void beforeElementForce(const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& f,
sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x) {}

virtual void computeElementsForces(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& f,
sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x) = 0;

void dispatchElementForcesToNodes(
Expand All @@ -103,13 +103,13 @@ class FEMForceField :
/// Methods related to addDForce
/// @{
void computeElementsForcesDeriv(const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& df,
sofa::type::vector<ElementGradient>& df,
const sofa::VecDeriv_t<DataTypes>& dx);

virtual void computeElementsForcesDeriv(
const sofa::simulation::Range<std::size_t>& range,
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& df,
sofa::type::vector<ElementGradient>& df,
const sofa::VecDeriv_t<DataTypes>& dx) = 0;

/**
Expand Down
4 changes: 2 additions & 2 deletions ...olidMechanics/FEM/Elastic/src/sofa/component/solidmechanics/fem/elastic/FEMForceField.inl
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Expand Up @@ -88,7 +88,7 @@ void FEMForceField<DataTypes, ElementType>::addForce(
template <class DataTypes, class ElementType>
void FEMForceField<DataTypes, ElementType>::computeElementsForces(
const sofa::core::MechanicalParams* mparams,
sofa::type::vector<ElementForce>& f,
sofa::type::vector<ElementGradient>& f,
const sofa::VecCoord_t<DataTypes>& x)
{
SCOPED_TIMER("ElementForces");
Expand Down Expand Up @@ -159,7 +159,7 @@ void FEMForceField<DataTypes, ElementType>::addDForce(

template <class DataTypes, class ElementType>
void FEMForceField<DataTypes, ElementType>::computeElementsForcesDeriv(
const sofa::core::MechanicalParams* mparams, sofa::type::vector<ElementForce>& df,
const sofa::core::MechanicalParams* mparams, sofa::type::vector<ElementGradient>& df,
const sofa::VecDeriv_t<DataTypes>& dx)
{
SCOPED_TIMER("ElementForcesDeriv");
Expand Down
122 changes: 7 additions & 115 deletions ...s/FEM/Elastic/src/sofa/component/solidmechanics/fem/elastic/impl/ElementStiffnessMatrix.h
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Expand Up @@ -25,125 +25,16 @@
#include <sofa/type/FullySymmetric4Tensor.h>
#include <sofa/component/solidmechanics/fem/elastic/impl/OrthotropicElasticityTensor.h>
#include <sofa/component/solidmechanics/fem/elastic/impl/StrainDisplacement.h>
#include <sofa/component/solidmechanics/fem/elastic/impl/trait.h>
#include <sofa/type/Mat.h>

#include <ostream>

namespace sofa::component::solidmechanics::fem::elastic
{

/**
* Specifies the type of matrix-vector product to be used with the stiffness matrix.
*/
enum class MatrixVectorProductType
{
/**
* The matrix-vector product is computed using the factorization of the matrix
*/
Factorization,

/**
* The matrix-vector product is computed using the dense matrix representation
*/
Dense
};

/**
* Represents an element stiffness matrix. It contains the dense matrix representation, but also
* its factorization. Both the factorization or the dense matrix can be used for the product of the
* stiffness matrix with a vector. Although it gives the same result, it has an impact on the
* performances.
*/
template <class DataTypes, class ElementType, MatrixVectorProductType matrixVectorProductType>
struct FactorizedElementStiffness
{
private:
using Real = sofa::Real_t<DataTypes>;
using FiniteElement = sofa::fem::FiniteElement<ElementType, DataTypes>;
static constexpr auto NbQuadraturePoints = FiniteElement::quadraturePoints().size();
static constexpr sofa::Size NumberOfIndependentElements = sofa::type::NumberOfIndependentElements<DataTypes::spatial_dimensions>;

/// The factors of the stiffness matrix
/// @{
std::array<StrainDisplacement<DataTypes, ElementType>, NbQuadraturePoints> B;
OrthotropicElasticityTensor<DataTypes::spatial_dimensions, sofa::Real_t<DataTypes>> elasticityTensor;
std::array<Real, NbQuadraturePoints> factors;
/// @}

/**
* The assembled stiffness matrix
*/
sofa::type::Mat<
ElementType::NumberOfNodes * DataTypes::spatial_dimensions,
ElementType::NumberOfNodes * DataTypes::spatial_dimensions,
sofa::Real_t<DataTypes>> stiffnessMatrix;

public:
const StrainDisplacement<DataTypes, ElementType>& getB(std::size_t i) const { return B[i]; }
Real getFactor(std::size_t i) const { return factors[i]; }
const OrthotropicElasticityTensor<DataTypes::spatial_dimensions, sofa::Real_t<DataTypes>>& getElasticityTensor() const { return elasticityTensor; }

void setElasticityTensor(
const sofa::type::FullySymmetric4Tensor<DataTypes::spatial_dimensions, sofa::Real_t<DataTypes>>& elasticityTensor_)
{
this->elasticityTensor.set(elasticityTensor_);
}

void addFactor(std::size_t quadraturePointIndex,
const Real factor,
const StrainDisplacement<DataTypes, ElementType>& B_)
{
this->factors[quadraturePointIndex] = factor;
this->B[quadraturePointIndex] = B_;

const auto K_i = factor * B_.multTranspose(elasticityTensor.toMat() * B_.B);
stiffnessMatrix += K_i;
}

const auto& getAssembledMatrix() const { return stiffnessMatrix; }

using Vec = sofa::type::Vec<
ElementType::NumberOfNodes * DataTypes::spatial_dimensions,
sofa::Real_t<DataTypes>>;

inline Vec operator*(const Vec& v) const
{
if constexpr (matrixVectorProductType == MatrixVectorProductType::Factorization)
{
if constexpr (NbQuadraturePoints > 1)
{
Vec result;
for (std::size_t i = 0; i < NbQuadraturePoints; ++i)
{
const auto& B = this->B[i];
result += B.multTranspose(this->factors[i] * (this->elasticityTensor * (B * v)));
}
return result;
}
else
{
return this->B[0].multTranspose(this->factors[0] * (this->elasticityTensor * (this->B[0] * v)));
}
}
else
{
return this->stiffnessMatrix * v;
}
}

friend std::ostream& operator<<(std::ostream& os, const FactorizedElementStiffness& obj)
{
return os << obj.getAssembledMatrix();
}

friend std::istream& operator>>(std::istream& in, FactorizedElementStiffness& obj)
{
return in;
}
};

template <class DataTypes, class ElementType, MatrixVectorProductType matrixVectorProductType = MatrixVectorProductType::Dense>
FactorizedElementStiffness<DataTypes, ElementType, matrixVectorProductType> integrate(
template <class DataTypes, class ElementType>
auto integrate(
const std::array<sofa::Coord_t<DataTypes>, ElementType::NumberOfNodes>& nodesCoordinates,
const sofa::type::FullySymmetric4Tensor<DataTypes::spatial_dimensions, sofa::Real_t<DataTypes>>& elasticityTensor)
{
Expand All @@ -154,8 +45,9 @@ FactorizedElementStiffness<DataTypes, ElementType, matrixVectorProductType> inte
static constexpr sofa::Size NumberOfNodesInElement = ElementType::NumberOfNodes;
static constexpr sofa::Size TopologicalDimension = FiniteElement::TopologicalDimension;

FactorizedElementStiffness<DataTypes, ElementType, matrixVectorProductType> K;
K.setElasticityTensor(elasticityTensor);
typename trait<DataTypes, ElementType>::ElementHessian K;

auto C = elasticityTensor.toVoigtMatSym().toMat();

std::size_t quadraturePointIndex = 0;
for (const auto& [quadraturePoint, weight] : FiniteElement::quadraturePoints())
Expand All @@ -180,7 +72,7 @@ FactorizedElementStiffness<DataTypes, ElementType, matrixVectorProductType> inte
dN_dq[i] = J_inv.transposed() * dN_dq_ref[i];

const auto B = makeStrainDisplacement<DataTypes, ElementType>(dN_dq);
K.addFactor(quadraturePointIndex, weight * detJ, B);
K += (weight * detJ) * B.multTranspose(C * B);

++quadraturePointIndex;
}
Expand Down
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