public override Matrix_Jagged IntegralArgument_Ke(Vector Xi)
{
int NNPE = ElementNodes.Length;
double Det_Jac;
Vector X;
Matrix_Jagged DNDX;
Matrix_Jagged Ke_Arg = new Matrix_Jagged(NNPE * 2, NNPE * 2);
Interpolator.Calculate_X_DNDX_DetJacobian(Xi, ElementNodes, out X, out DNDX, out Det_Jac);
for (int p = 0; p < NNPE; p++)//p defines node number
{
Node_ND_Unknowns_VectorField Unknown_p = (Node_ND_Unknowns_VectorField)ElementNodes[p].Unknowns;
int NDFp = Unknown_p.UnknownDoFs.Length;
for (int i = 0; i < NDFp; i++) //loop at x direction
{
for (int q = 0; q < NNPE; q++) //
{
Node_ND_Unknowns_VectorField Unknown_q = (Node_ND_Unknowns_VectorField)ElementNodes[q].Unknowns;
int NDFq = Unknown_q.UnknownDoFs.Length;
for (int j = 0; j < NDFq; j++)//loop at y direction
{
double temp = 0;
for (int m = 0; m < 2; m++) //loop at x direction
{
for (int n = 0; n < 2; n++) //loop at y direction
{
double Eimjn = 0;
Eimjn = GetE(i, m, j, n);//obtain constitutive matrix
temp += DNDX.Values[p][m] * Eimjn * DNDX.Values[q][n];
}
}
Ke_Arg.Values[NDFp * p + i][NDFq * q + j] = temp * Det_Jac; //store Ke
}
}
}
}
return(Ke_Arg);
}