Hwat does the trade equation look like?

[Martin the Dane]

I have been playing Freeciv a bit, but have not been able to figure out how the trade system works. Could anyone supply the equation, or just the factors in determening the benefit fo creating trade routes. As it is now, I almost exclusevly use Caravans/Freights to build wonders.

Martin the Dane

[Jing]

In Freeciv, the trade bonus is calculated as following:

( trade of city #1 + trade of city #2 + 4) / 8

If both cities are on the same continent, the bonus is reduced by half.
If both cities belong to the same player, the bonus is also reduced by half.

The one time gold/science bonus is calculated as following:

(trade of city #1 + trade of city #2) * (distance between cities + 10) / 24

The same reduction factors apply as above.
In addition, once the player discovers Railroad, the one time bonus is reduced by 1/3 (i.e. multiplied by 2/3). It is multiplied by 2/3 again when the player discovers Flight.

Compared to Civ2, traderoutes are severely under valued in Freeciv. That's why they are seldomly used, if ever. I once submitted a patch to correct the situation, but it never got into CVS. Neither did the modified version by the then administrator, as I just found out to my dismay. But fear not, I am ready to try again as soon as I get reliable infomation on how exactly it is handled in Civ2.

[CapTVK]

I can help you with that Jing. Although I must warn you that the trading model in civ2 is very similar to the first one. The demand and type of resources now play a role in the gold/science bonus (trade arrows remain the same). I would rather see the resource model ala Civ3 implemented directly. But we should aim for civ2 first.

[Martin the Dane]

I would rather see the resource model ala Civ3 implemented directly.

Is that somthing like the CTP model, or has someone actually come up with something that resembles trade?

Why not use a system where only goods found within the city perimeter can be sold, including food. So that the city selling the stuff, would gain gold, for whatever is sold, while the recieving city, will gain the trade good.

[Jing]

Thanks, CapTVK. I have already received reliable info on the Civ2 model. However, I am not going to try to implement the supply and demand system, as it is generally considered too cumbersome by those who came before me. All I want to do is to correct some of the mistakes in the current implementation, thus make trade routes more relevant in the game. So in the end, it will still be the watered down version of the Civ2 model as it is now, but with numbers more inline with Civ2.

The mistakes in the current code are:

--The trade bonus should be double the base amount if the cities are on different continents.
--The one time gold/science bonus is not affected by whether the cities belong to the same player or are on the same continent.

Without the supply and demand system, the one time bonus could only be apprximate. A fudge factor of 3 seems to be a reasonable compromise.

I believe most of these were in the modified patch by Jeff. All I have to do is to update it and submit it again.

[CapTVK]

Originally posted by Martin the Dane

Is that somthing like the CTP model, or has someone actually come up with something that resembles trade?

Why not use a system where only goods found within the city perimeter can be sold, including food. So that the city selling the stuff, would gain gold, for whatever is sold, while the recieving city, will gain the trade good.

Martin,

Trade is far more important now in Civ3. You now need resources to build specific units (e.a battleship needs iron+coal). Combined with colonies (a bit like the depots in RR) that can be established outside your cities trade will become very important.

I wonder how this could be implemented in Freeciv. It would require a completely new trading systems plus new resource squares.

Think along the lines of Civ and Railroad Tycoon combined.

Jing,

What do you mean by a fudge factor of 3? Is the bonus multiplied by 3x?

[Jing]

What do you mean by a fudge factor of 3? Is the bonus multiplied by 3x?

That's correct. This is because the base amount is multiplied by 2 anyway in the calculation towards the final bonus ammount, and when the demand is met the payoff is even bigger. In the end, a multiplier of 3 is a conservative but reasonable compromise, IMHO.