public void CalculateEigenvalueDecomposition() { double[] i = new double[3]; double[] j = new double[3]; double[] k = new double[3]; double[] u = new double[3]; double[] t_vol = new double[3]; double[] vol = new double[3]; vol[0] = 0; vol[1] = 0; vol[2] = 0; double[] func_sum = new double[3]; func_sum[0] = 0; func_sum[1] = 0; func_sum[2] = 0; double[] func_sum_inertia = new double[3]; func_sum_inertia[0] = 0; func_sum_inertia[1] = 0; func_sum_inertia[2] = 0; double func_sum_xy = 0; double func_sum_xz = 0; double func_sum_yz = 0; double surfaceArea = 0; //loop through all the triangles for (int count = 0; count < _connections.Length; count++) { //get the 3 points of the triangle double[] p1 = new double[3]; double[] p2 = new double[3]; double[] p3 = new double[3]; //Fix so its relative to the centroid center of mass p1[0] = (double)_pts[_connections[count][0]][0] - _centroid[0]; //fix x's first p2[0] = (double)_pts[_connections[count][1]][0] - _centroid[0]; p3[0] = (double)_pts[_connections[count][2]][0] - _centroid[0]; p1[1] = (double)_pts[_connections[count][0]][1] - _centroid[1]; //fix y's p2[1] = (double)_pts[_connections[count][1]][1] - _centroid[1]; p3[1] = (double)_pts[_connections[count][2]][1] - _centroid[1]; p1[2] = (double)_pts[_connections[count][0]][2] - _centroid[2]; //fix z's p2[2] = (double)_pts[_connections[count][1]][2] - _centroid[2]; p3[2] = (double)_pts[_connections[count][2]][2] - _centroid[2]; //calculate the i, j, k vectors i[0] = p2[0] - p1[0]; j[0] = p2[1] - p1[1]; k[0] = p2[2] - p1[2]; i[1] = p3[0] - p1[0]; j[1] = p3[1] - p1[1]; k[1] = p3[2] - p1[2]; i[2] = p3[0] - p2[0]; j[2] = p3[1] - p2[1]; k[2] = p3[2] - p2[2]; //cross product between two vectors, to determine normal vector u[0] = j[0] * k[1] - k[0] * j[1]; u[1] = k[0] * i[1] - i[0] * k[1]; u[2] = i[0] * j[1] - j[0] * i[1]; //Normalize vector to 1 double norm = Math.Sqrt(u[0] * u[0] + u[1] * u[1] + u[2] * u[2]); if (norm != 0.0) { u[0] = u[0] / norm; u[1] = u[1] / norm; u[2] = u[2] / norm; } else { u[0] = 0.0; u[1] = 0.0; u[2] = 0.0; } //This is reduced to ... //area of a triangle... double a = Math.Sqrt(i[1] * i[1] + j[1] * j[1] + k[1] * k[1]); double b = Math.Sqrt(i[0] * i[0] + j[0] * j[0] + k[0] * k[0]); double c = Math.Sqrt(i[2] * i[2] + j[2] * j[2] + k[2] * k[2]); double s = 0.5 * (a + b + c); double area = Math.Sqrt(Math.Abs(s * (s - a) * (s - b) * (s - c))); //patches(count,1) = area // surfaceArea += area; //volume elements ... double zavg = (p1[2] + p2[2] + p3[2]) / 3.0; double yavg = (p1[1] + p2[1] + p3[1]) / 3.0; double xavg = (p1[0] + p2[0] + p3[0]) / 3.0; //sum of function for centroid calculation func_sum[0] += t_vol[0] * xavg; func_sum[1] += t_vol[1] * yavg; func_sum[2] += t_vol[2] * zavg; //sum of function for inertia calculation func_sum_inertia[0] += area * u[0] * xavg * xavg * xavg; func_sum_inertia[1] += area * u[1] * yavg * yavg * yavg; func_sum_inertia[2] += area * u[2] * zavg * zavg * zavg; //sum of function for products of inertia calculation func_sum_xz += area * u[0] * xavg * xavg * zavg; func_sum_xy += area * u[1] * yavg * yavg * xavg; func_sum_yz += area * u[2] * zavg * zavg * yavg; } func_sum_inertia[0] /= 3; func_sum_inertia[1] /= 3; func_sum_inertia[2] /= 3; double Ixy = -1 * func_sum_xy / 2; double Ixz = -1 * func_sum_xz / 2; double Iyz = -1 * func_sum_yz / 2; double Iyx = Ixy; double Izx = Ixz; double Izy = Iyz; double Ixx = func_sum_inertia[1] + func_sum_inertia[2]; double Iyy = func_sum_inertia[0] + func_sum_inertia[2]; double Izz = func_sum_inertia[0] + func_sum_inertia[1]; GeneralMatrix i_CoM = new GeneralMatrix(3, 3); i_CoM.Array[0][0] = Ixx; i_CoM.Array[0][1] = Ixy; i_CoM.Array[0][2] = Ixz; i_CoM.Array[1][0] = Iyx; i_CoM.Array[1][1] = Iyy; i_CoM.Array[1][2] = Iyz; i_CoM.Array[2][0] = Izx; i_CoM.Array[2][1] = Izy; i_CoM.Array[2][2] = Izz; EigenvalueDecomposition eig = i_CoM.Eigen(); _eigenvalues = eig.D; _eigenvectors = eig.GetV(); //make sure this is a right handed matrix if (_eigenvectors.Determinant() < 0) { _eigenvectors = _eigenvectors.Multiply(-1); } }