[Freeciv-Dev] Re: (PR#13683) Reducing the upgrade cost

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=13683 >

Tying the bonus to techs seems like a good solution to me.  These 
bonuses are pretty small and should act to just decrease costs slowly 
over time.

However the bonus should not affect the 2*missing part of the upgrade 
cost.  It should never be possible to drop the cost below (2 gold) * 
(the difference in shield costs).  The bonus should only affect the 
squared part of the calculation.  We could even make it affect the 
*exponent* of this calculation so it became

   eft = get_player_bonus(pplayer, EFT_UPGRADE_COST);
   cost = 2 * missing + 20 * power(missing, (double)eft / 100.0);

or for extra points the 20 could be put into the ruleset as well.

   eft = get_player_bonus(pplayer, EFT_UPGRADE_EXPONENT);
   eft2 = get_player_bonus(pplayer, EFT_UPGRADE_MULTIPLIER);
   cost = 2 * missing + eft2 * power(missing, (double)eft / 100.0);

Note that these values are actually inside unit_buy_gold_cost and should 
probably remain there - so changes here will decrease unit purchase 
costs too.

-jason