[Mathematical   Expression   2](Subscript[F, a])(x,y)=(1/((Sqrt[2π])σ))(e^(-(((x^2)+(y^2))/(2(σ^2)))))
                                                                         [Mathematial   Expression   3](Subscript[F, d])(x,y)=cos(((π(Sqrt[(x^2)+(y^2)]))/k))/N
                                                                         [Mathematial   Expression   4](Subscript[F, s])(x,y)=(cos^n)(((π(Sqrt[(x^2)+(y^2)]))/k))/(N^n)