Many objects---cylinders, spheres, planes---recur in E&M. You might need B, V, or E, etc.
It would save time (though increase complexity) to add each common object as a vertex, with no incoming edges, and with outgoing edges providing the actual expression for each quantity pointing to the corresponding vertex.
They could be added like any physical quantity; their lack of incoming edges would arise naturally from their not appearing in any equations.
Many objects---cylinders, spheres, planes---recur in E&M. You might need B, V, or E, etc.
It would save time (though increase complexity) to add each common object as a vertex, with no incoming edges, and with outgoing edges providing the actual expression for each quantity pointing to the corresponding vertex.
They could be added like any physical quantity; their lack of incoming edges would arise naturally from their not appearing in any equations.