“…In this section a brief introduction to the discretization of physical quantities and to the discretization of the exterior derivative is presented. For a more detailed presentation the reader is directed to [2,4,6] Consider a three dimensional domain Ω and an associated grid consisting of a collection of points, τ (0),i , line segments connecting the points, τ (1),i , surfaces bounded by these line segments, τ (2),i , and volumes bounded by these surfaces, τ (3),i .…”