[Freeciv-Dev] [RFC] Tech costs and AI problem

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

Working on the tech cost patch I encountered the following problem:
ai/advmilitary.c:process_defender_want() contains

    k = pplayer->ai.num_unknown_techs[unit_types[i].tech_requirement];
    ...
    l = k * (k + pplayer->research.techs_researched) * game.researchcost /
       (game.year > 0 ? 2 : 4); /* cost (shield equiv) of gaining these techs */

K is the number of techs which have to researched till the goal tech
(unit_types[i].tech_requirement) _can_ be researched/is reachable.

Note that currently

int total_bulbs_required(struct player *pplayer)
{
  int timemod = (game.year > 0) ? 2 : 1;

  return timemod * pplayer->research.techs_researched * game.researchcost;
}

So I assume that the condition in the AI code can wants to mimic this.

I want to compute l from a call to total_bulbs_required_for_goal
(which is the new method for this).

If we assume that
  s=pplayer->research.techs_researched,
  rc=game.researchcost and 
  tbrfg=the result from the total_bulbs_required_for_goal 
than the old method will compute:

 l_old = (k*k + k*s) * rc
the new method calculates correctly:
 tbrfg = (0.5*k*k + (s - 0.5)*k) * rc

So for large k's a good approximation would be "l_new = tbrfg / 2" but this
fails for small ks:
 l_old(k=1) = (s + 1)*rc
 l_new(k=1) = (s*rc)/2

 l_old(k=2) = (2*s + 4)*rc
 l_new(k=2) = ((s + 1)*rc)/2

I would have no problems if these numbers wouldn't get mixed with
build_costs and the number of cities.

So any advise from the "AI-people"?

        Raimar

-- 
 email: rf13@xxxxxxxxxxxxxxxxx
 "Premature optimization is the root of all evil."
    -- D. E. Knuth in "Structured Programming with go to Statements"