[SolidMechanics][FEM] Fix FastTetrahedralCorotationalForceField stiffness matrix assembly (sofa-framework#6154)

th-skam · web-flow · commit 8064720f0ae9 · 2026-06-26T09:16:39.000+09:00
diff --git a/Sofa/Component/SolidMechanics/FEM/Elastic/src/sofa/component/solidmechanics/fem/elastic/FastTetrahedralCorotationalForceField.inl b/Sofa/Component/SolidMechanics/FEM/Elastic/src/sofa/component/solidmechanics/fem/elastic/FastTetrahedralCorotationalForceField.inl
@@ -556,7 +556,7 @@ void FastTetrahedralCorotationalForceField<DataTypes>::buildStiffnessMatrix(
     for(sofa::Size i=0; i < nbEdges; ++i )
     {
         const auto& edge = edges[i];
-        dfdx(3 * edge[0], 3 * edge[1]) += -edgeDfDx[i];
+        dfdx(3 * edge[0], 3 * edge[1]) += -edgeDfDx[i].transposed();
         dfdx(3 * edge[1], 3 * edge[0]) += -edgeDfDx[i];
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -556,7 +556,7 @@ void FastTetrahedralCorotationalForceField<DataTypes>::buildStiffnessMatrix(`
`556`	`556`	`for(sofa::Size i=0; i < nbEdges; ++i )`
`557`	`557`	`{`
`558`	`558`	`const auto& edge = edges[i];`
`559`		`- dfdx(3 * edge[0], 3 * edge[1]) += -edgeDfDx[i];`
	`559`	`+ dfdx(3 * edge[0], 3 * edge[1]) += -edgeDfDx[i].transposed();`
`560`	`560`	`dfdx(3 * edge[1], 3 * edge[0]) += -edgeDfDx[i];`
`561`	`561`	`}`
`562`	`562`	`}`