Baby's first FEM simulation

a4.cxx

      // Need to compute:
      //*************************ASSIGNMENT 4 START HERE*******************
      matd = Vec3DiffMatrix3x3::createFromColumnVectors(xEl[1] - xEl[0], xEl[2] - xEl[0], xEl[3] - xEl[0]);

      //Compute the deformation gradient F = d*D^{-1}
      matF = matd * matDInv();
                  

      //Get the second Piola Kirchoff stress from your element
      //Place the value in matS
      computeSecondPiolaKirchhoff(matS, matF, matParams);

      //compute 1st Piola Kirchoff stress
      matP = matF*matS;
            
      //Compute nodal forces
      //nodalForces[0] = 3x1 column vector of nodal forces acting on node 0
      //nodalForces[1] = 3x1 column vector of nodal forces acting on node 1
      //nodalForces[2] = 3x1 column vector of nodal forces acting on node 2
      //nodalForces[3] = 3x1 column vector of nodal forces acting on node 3
      // f[m]_n = (V0 * matP * D^-T)_nm
      Vec3DiffMatrix3x3 matDinvTrans = matDInv.transposed();
      Vec3DiffMatrix3x3 forceMatrix = (V0 * matP * matDinvTrans);
      for (unsigned col=1; col < 4; col++){
        nodalForces[col] = forceMatrix.getColumnVector(col-1);
      }

      nodalForces[0] = -1*(nodalForces[1] + 
                           nodalForces[2] + 
                           nodalForces[3]);
      
      //************************ASSIGNMENT 4 END HERE******************************