Paving: a new implementation of dual-bound resistance calculations

Dual-bound field calculations by the tube-and-slice (TAS) method require internal subdivision of the quadrilaterals that define the flow tubes and the potential slices. Paving is a direct calculation, using the quadrilateral vertices and without subdivision, that delivers bounds for each quadrilateral independently. This local measure of paving quality allows local improvement, by finer subdivision and by moving vertices under mouse control, so overall bound separation can be tightened. A new statistical approach links the ratio of upper and lower bounds with the variance of the quadrilateral angles