<URL: http://bugs.freeciv.org/Ticket/Display.html?id=39949 >
This report is about something that I saw Freeciv's AI do in one
of my games a few years ago. I've never bothered to report it
because it is not a big problem.
I'm reporting it now because I think that it is an interesting
AI problem. Furthermore I've never seen this problem mentioned in
any other bug reports. If it has already been solved in Freeciv,
then I apologize for the duplicate problem report.
Here is a the description of the problem:
I was playing on a hex tileset. It was early in the game. I
had a size 2 city on plains. At the end of one turn, two enemy (AI)
chariots moved into one of the outermost tiles of that city (two
tiles away from my city center).
IIRC, the AI already knew where my city center was. So I
assumed that those chariots were headed towards it to capture it.
Coincidentally, my city had just finished making a phalanx on
that same turn. So, because it was new, that phalanx did not have
time to finish fortifying itself before the next turn.
My city did *not* have city walls. And I had no other units
nearby that could reach my city (to reinforce it) before the
chariots could attack it (on the next turn).
The future looked bleak for my city and its phalanx.
I figured that the phalanx (that was in my city) might survive
one attack from a chariot. But it seemed unlikely that that phalanx
would survive two chariot attacks on the same turn. And, if that
phalanx lost either chariot battle, then my city would fall into
enemy hands.
Since I couldn't save the city, I decided to save the phalanx.
I moved it out of the city center and onto an adjacent mountain
tile.
That left the city undefended. So, on the next turn, one of
the enemy chariots could have just marched into my city and
captured it.
But that is *not* what happened. Instead, on the next turn,
both chariots attacked the phalanx on the mountain. Both chariots
lost their battles. So both the city and the phalanx survived.
Why did this happen? I believe that it was a combination of two
factors:
1) Zone of control (ZOC) exerted by the phalanx restricted the
movements of the chariots.
2) The AI could not see the circumvention to that ZOC movement
restriction.
The following map may help explain this situation:
____
/ \
____/ A \____
/ \ / \
/ D \____/ B \____
\ / \ / \
\____/ E \____/ C \
/ \ / \ /
/ H \____/ F \____/
\ / \ / \
\____/ I \____/ G \
/ \ / \ /
/ K \____/ J \____/
\ / \ / \
\____/ L \____/ \
\ / \ /
\____/ \____/
The city and the phalanx were in tile I. The chariots first
became visible to the city when they entered tile B.
Tiles C and G were ocean. Tile F was mountain. The rest of the
tiles were flat terrain (grassland, plains, etc.). There were no
roads on any of these tiles except for I (i.e. the city's center).
The phalanx evacuated from the city by moving from I to F. On
the next turn, instead of heading towards the city, both chariots
attacked from B to F (i.e. they attacked the phalanx on the
mountain). And, as I said, both chariots lost that battle.
(Why would chariots attack a phalanx on a mountain anyway?
Because it was there? :-) But that is a different AI problem.)
So apparently the AI did not see the tactic that many human
players would see. I.e. first move one chariot from B to A and then
move that same chariot from A to E.
Then move the second chariot from B to E (which the phalanx's
ZOC no longer blocks - because of the chariot now sitting on E) and
then from E to I (which the phalanx's ZOC does not block because it
is a move *into* a city).
This tactic is somewhat analogous to an ant bridge. I.e. some
ants will use their bodies to bridge a gap in their path so that
other ants can cross over that gap (by walking across the bridge
that consists of the other ants' bodies - i.e. an "ant bridge").
If the AI had done that, then I would have been impressed. But
it didn't. Too bad. (Maybe Freeciv's AI is smarter now. I don't
know because I haven't tested it lately.)
It seemed to me that this is an interesting challenge for an AI.
So I'm finally posting about it now - in case there is someone out
there who might be interested in tackling this problem.
I don't have that saved game anymore (so I'm describing this
situation from memory). I hope that I have described it correctly
and that the description makes sense. If not, then please post any
questions that you have about it.
Sorry about the lack of a saved game. FWIW I suspect that that
saved game might be too out of date by now to be useful anyway. I
assume that this situation can easily be recreated and tested by
using Freeciv's editing capabilities. I hope so.
HTH.
-Eddie
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