[thanatropism]

When we have semi-complicated models we try to factor out the harder part to run outside Excel -- and thus have programming utilities available -- and write "front-end" logic (currency conversions, inflation adjustments, charts, etc.) in Excel. I work a lot with Matlab, and this is really to use with the .xlam add-in provided. The trick is to figure out the division between the "back-end part" (that needs debugging tools, tests, etc.) and the "spreadsheet part" (that can take an understandable, but black-boxed/stored-as-values input and do spreadsheet logic that's flexible enough for the guys who need to mess with that).