@quantensalat @ethanjstark @NanoRaptor my advisor had a nightmarish Excel spreadsheet of unknown provenance that he loved to show off to prospective students (and *only* them??) that…acted as a magnetostatic field solver
Some number of cells (maybe it was flexible and you could configure the bounds?) represented the computational domain, and you populated the cells, one symbol for non-linearities (iron) and another for current sources/sinks
then click "step" a bunch of times until it converged