poisson_sym(V,X,coo​rdinate_system)

This Function calculates the double derivative (Poisson's Equation) of the 3D symbolic vector in Cartesian, Cylindrical, and Spherical coordinate system.
function poissonSym = poisson_sym(V,X,coordinate_system)
V is the 3D symbolic vector field
X is the parameter which the divergence will calculate with respect to.
coordinate_system is the kind of coordinate system at which the vector field is specified.
The Poisson's Equation is calculated according to (Engineering Electromagnetics Sixth Edition William H. Hayt, Jr. . John A. Buck)
Example (1):
V=4*y*z/(x^2+1)
Del_2_V=poisson_sym(V,[x y z],'Cartesian')
Example (2):
V=5*rho^2*cos(2*phi)
Del_2_V=poisson_sym(V,[rho phi z],'Cylindrical')
Example (3):
V=2*cos(phi)/r^2;
Del_2_V=poisson_sym(V,[r theta phi],'Spherical')