Question on offers on Distributed Exchange

Question

SOVED: I thought Test2 was buying 3 AXX, but in fact it was selling 3 XLM. Don't forget to check the ordering and meaning of parameters!

I'm having trouble explaining what's going on with my bid and offers:

Issuer: GD57JZ42YKIEDLCFIZD2BW6LIYN7KIOEMFSIL37WZ5RS7DPLEW6DOOWG
Asset: AXX

Test1: GC5RQZPRI2SXMOL5JP2QTJXO72IAJLGMNU7TG5ADU6OMYDEJI3APJTZI
Balance: 444 AXX

Test2: GBPJWQBGYSIWHFDLDKNO4XMHUC7RUOX7GBORLG4ZKUFGKWMPW77OIHXA
Balance: 77 AXX

They each create an offer:

Test1: sell 20 AXX
Test2: buy 3 AXX

What I expected to happen is:

Test1 balance: 441 AAX (444 - 3)
Test2 balance: 80 AAX  (77 + 3)
Sell offer: 17 AXX     (20 - 3)

What actually happened was:

Test1 balance: 424 AAX (444 - 20)
Test2 balance: 97 AAX  (77 + 20)
Buy offer: 2.9 AAX     (3 - 0.1)

...

So my questions are:

• Why did Test2 get 20 AAX when it only wanted 3?
• Why is there a buy offer of 2.9 AAX?

I'm hoping this is just my misunderstanding of the documentation.

Edit: Here's the links to operations for Test1 and Test2:

https://www.stellar.org/laboratory/#explorer?resource=operations&endpoint=for_account&values=eyJhY2NvdW50X2lkIjoiR0M1UlFaUFJJMlNYTU9MNUpQMlFUSlhPNzJJQUpMR01OVTdURzVBRFU2T01ZREVKSTNBUEpUWkkifQ%3D%3D&network=test

https://www.stellar.org/laboratory/#explorer?resource=operations&endpoint=for_account&values=eyJhY2NvdW50X2lkIjoiR0JQSldRQkdZU0lXSEZETERLTk80WE1IVUM3UlVPWDdHQk9STEc0WktVRkdLV01QVzc3T0lIWEEifQ%3D%3D&network=test

And as you can see, the trades for Test2 indicate taking 20 and not 3?

https://www.stellar.org/laboratory/#explorer?resource=trades&endpoint=for_account&values=eyJhY2NvdW50X2lkIjoiR0M1UlFaUFJJMlNYTU9MNUpQMlFUSlhPNzJJQUpMR01OVTdURzVBRFU2T01ZREVKSTNBUEpUWkkifQ%3D%3D&network=test

https://www.stellar.org/laboratory/#explorer?resource=trades&endpoint=for_account&values=eyJhY2NvdW50X2lkIjoiR0JQSldRQkdZU0lXSEZETERLTk80WE1IVUM3UlVPWDdHQk9STEc0WktVRkdLV01QVzc3T0lIWEEifQ%3D%3D&network=test

Answer 1

From the MANAGE_OFFER docs:

Price {numerator, denominator} Price of 1 unit of selling in terms of buying. For example, if you wanted to sell 30 XLM and buy 5 BTC, the price would be {5,30}.

The price in the offer of Test1 account is:

{
  "n": 1,
  "d": 250
}

and it's selling AXX and buying XLM (native). To translate this: Test1 wants to sell 250 AXX for 1 XLM (in that ratio/price). It wants to sell 20 AXX so it will get (if the offer is fully consumed):

250 AXX - 1 XLM
 20 AXX - x XLM

 x = 20 * 1 / 250 = 0.08

The opposite offer's price (Test2 offer) is exactly an inverse (250/1) and selling 3 XLM for AXX:

250 AXX - 1 XLM
  x AXX - 3 XLM

 Test2 can by up to:
 x = 3 * 250 / 1 = 750

It means that the Test1's offer will be fully consumed because amount required to fully consume this offer is just 0.08 XLM and Test2 is selling 3 XLM. Also it can buy up to 750 AXX but Test1 is selling only 20 AXX. So after the trade happens we have:

Test 1 XLM balance += 0.08
Test 1 AXX balance -= 20
Test 1 offer: fully consumed

Test 2 XLM balance -= 0.08
Test 2 AXX balance += 20
Test 2 offer: still selling 2.92 XLM (it only sold 0.08 XLM)