In vector calculus, the divergence is an operator that measures the magnitude of a vector field's source or sink
at a given point; the divergence of a vector field is a (signed) scalar. For example, consider air as it is heated
or cooled. The relevant vector field for this example is the velocity of the moving air at a point. If air is heated
in a region it will expand in all directions such that the velocity field points outward from that region. Therefore
the divergence of the velocity field in that region would have a positive value, as the region is a source. If the
air cools and contracts, the divergence is negative and the region is called a sink. More technically, the divergence
represents the volume density of the outward flux of a vector field from an infinitesimal volume around a given
point.  Wikipedia
"Ñ" is a vector and is pronounced "del." The vector function is A(x,y,z),
A(r,Φ,z), or A(r,θ,Φ)
Cartesian Coordinates 

Cylindrical Coordinates 

Spherical Coordinates 

