# itk::fem updating displacements

Dear ITK users,

I have another question. In order to visualize the deformation, I want to replace the old node coordinates with the new one after generating the solution, like in UpdateDisplacements() function in itkFemSolver.hxx 610-651
The code-block, which generates solution:

``````m_FemSolver->Update();
//m_FemSolver->UpdateDisplacements();
const unsigned int invalidId= itk::fem::Element::InvalidDegreeOfFreedomID;
int numberOfNodes= m_FemSolver->GetInput()->GetNumberOfNodes();

for(int i= 0; i< numberOfNodes; i++)
{
itk::fem::Element::Node::Pointer node= m_FemSolver->GetInput()->GetNode(i);
std::cout<<"FEM Mesh Node: "<< node->GetGlobalNumber() << " Coordinates: "<< node->GetCoordinates()<<std::endl;

for(unsigned int j= 0, dof; (dof= node->GetDegreeOfFreedom(j))!= invalidId; j++)
{
cout <<"FEM Mesh Solution: "<< m_FemSolver->GetSolution(dof)<<endl;
}
}
``````

gives me following output, that shows, I have some solutions for nodes 69 and 70:

``````FEM Mesh Node: 68 Coordinates: -61.1098 -139.262 211.9
FEM Mesh Node: 69 Coordinates: -61.0742 -139.319 211.9
FEM Mesh Solution: 82.6806
FEM Mesh Solution: -32.5517
FEM Mesh Solution: 6.36021
FEM Mesh Node: 70 Coordinates: -61.3429 -138.832 211.9
FEM Mesh Solution: 0.798099
FEM Mesh Solution: 37.6971
FEM Mesh Solution: -4.36149
FEM Mesh Node: 71 Coordinates: -61.5039 -138.402 211.509
FEM Mesh Node: 72 Coordinates: -61.6232 -138.402 211.9
``````

if I want to update the displacements:

``````//itk::fem::LinearSystemWrapper::Pointer wrapper;
VectorType replacedNodeVector(3);
for(int i= 0; i< numberOfNodes; i++)
{
TetrahedronNodeType::Pointer node= m_FemSolver->GetInput()->GetNode(i);
//itk::fem::Element::Node::Pointer node= m_Fem3dSolver->GetInput()->GetNode(i);

for(unsigned int j= 0; j< 3; j++)
{
std::cout<<"FEM Mesh Solution Vector: "<<m_FemSolver->GetSolution(node->GetDegreeOfFreedom(j))<<std::endl;
replacedNodeVector[j] = node->GetCoordinates()[j] +  m_FemSolver->GetSolution(node->GetDegreeOfFreedom(j));
//replacedNodeVector[j] = node->GetCoordinates()[j] + m_ls->GetSolutionValue(node->GetDegreeOfFreedom(j));
}
node->SetCoordinates(replacedNodeVector);
std::cout<<"FEM Mesh New Node: "<< node->GetGlobalNumber() << " Coordinates: "<< node->GetCoordinates()<<std::endl;
}
``````

I get as output:

``````FEM Mesh New Node: 67 Coordinates: -61.0742 -139.262 211.797
FEM Mesh Solution Vector: 0
FEM Mesh Solution Vector: 0
FEM Mesh Solution Vector: 0
FEM Mesh New Node: 68 Coordinates: -61.1098 -139.262 211.9
FEM Mesh Solution Vector: 82.6806
FEM Mesh Solution Vector: -32.5517
FEM Mesh Solution Vector: 6.36021
FEM Mesh New Node: 69 Coordinates: 21.6064 -171.871 218.26
FEM Mesh Solution Vector: 0.798099
FEM Mesh Solution Vector: 37.6971
FEM Mesh Solution Vector: -4.36149
FEM Mesh New Node: 70 Coordinates: -60.5448 -101.135 207.539
FEM Mesh Solution Vector: 0
FEM Mesh Solution Vector: 0
FEM Mesh Solution Vector: 0
``````

My questions are:
Do I do it correct for the replacements, if I sum the old node coordinate with the generated solution vector for that spacial node?:

``````replacedNodeVector[j] = node->GetCoordinates()[j] + m_FemSolver->GetSolution(node->GetDegreeOfFreedom(j));
``````

In my test application, I apply some force at node 1( loadNode->SetNode(1); ) but in generated solution it shows that the force doesn’t act on node 1 and nodes around it but for nodes 68, 69, 82, and 83. All the other solutions are zero. My test mesh contains 86 nodes and 162 elements. If I want to apply the force except node 1,eg at node 20, I get then segmentation fault.

``````typedef itk::fem::LoadNode LoadNodeType;