alors pour les pts d'arenes c simple :
Team A's Current Score: 1500pt
Team A's Chance of Winning: 1500 / (1500 + 1580) = .48701
Team B's Current Score: 1580pt
Team B's Chance of Winning: 1580 / (1500 + 1580) = .51298
Now Let's say Team A won the battle then
Team A's New Score: 1500 + 100*(1-.48701) = 1500 + 51.299 = 1551.299
Team B's New Score: 1580 + 100*(0-.51298) = 1580 + -51.298 = 1528.71
Now Let's say Team B won the battle then
Team A's New Score: 1500 + 100*(0-.48701) = 1500 + -48.701 = 1451.299
Team B's New Score: 1580 + 100*(1-.51298) = 1580 + 48.701 = 1628.701
As you can see when a team with a higher ranking score wins a match against a lower ranking team they receive fewer points then if the lower rank team won. Such a system allows newly formed teams to quickly gain rank as they fight teams with much better scores then them.
Unlike the current honor system there will be a matching system which sets up teams with similar scores. This was the main problem with the current honor system since pre-made teams of epic equipped people were able to gain large amounts of honor by farming those with lesser gear. In the arena system, gear will still matter but teams will eventually only gain more points by wining against those with similar gear.
Blizzard has said on the Arena rating system that the rating point will not decay overtime even for an extended period.
Arena Point Calculation
The transformation from your Team Rating to Arena Points starts off as a linear function, but once you go beyond a certain rating threshold, the function becomes logistic. This means that you will see a significant payoff increase once your Team Rating goes beyond a certain point, but the high-end spectrum of the ratings will eventually notice a decrease in how much bang they get for their buck. You can stockpile a maximum of 5,000 Arena Points.
Formulas:
X = Team Rating, Y = Arena Points
If X>1500: Y = 2894/(1+259*e^(-0.0025*X))
Else: Y = 0.206*X+99