//Ф(j) with integer j
double Elem(int j);

//Ф(j) with half-integer j
double Elem(double j);

// d/dx Ф(j) with integer j
double diffElem(int j);

// d/dx Ф(j) with half-integer j
double diffElem(double j);

double Solution()
{
    Elem(1) + Elem(0.5)
}

double diffSolution()
{
    diffElem(1) + diffElem(0.5)
}