Need to update goal function to make reducing taxes be desirable

[wscott]

The current model has a 'minimum' spending level and sets up the constraints so that every year has at least that much money to spend. The model maximizes that min spending level.

But this leaves a lot of decisions unconstrained as we probably only have some years that are critical for that min level and other years where the spending options don't matter as much. We should add a secondary constraint that the model minimizes the amount of taxes paid.

Like max: spending + total_tax / years / 10

Or perhaps maximizing the money left at the end will do the same thing...

[wscott]

Actually, we don’t really want to minimize taxes. We want more money. This seems better:

maximize: min_spending + ave_spending/10

The goal is a reliable spending target but after that we want the extra money maximized.

[wscott]

#18 attempts to fix this.

[wscott]

And that fix didn't really work.