Calculate yVault APY

gistfile1.txt

Number of tokens within an yVault is calculated for the first time by

[number  of token outside of yVault] / [factor] = [number of token within yVault]

Then the number inside the yVault is updated by simple multiplication by a multiplication factor:

[old number of token outside of yVault]  * [factor] = [new number of token within yVault]

Since old number doesn't change, and only the factor does, it is enough to compare the % difference between two factors over different lengths to get the % change of the investment. 
    (500 * 10 = 5000) ,500 * (10*10%=11) = 550 [= 500*10%]
 _

this [factor] is the same in every contract, [getPricePerFullShare]

Now, we take snapshots at given intervals and call the function getPricePerFullshare.

Let's say each 5 min, 288 times (= 24hs)

then we calculate the daily continuous compounding interest rate like so:

i = ln (n2/n1)/288

So, that is the continuously compounding interest rate for one single day, if we have have more than 288 values (because we're trying to update the apy value every x minutes,  we just take the last one (n[-1]) and the 287th last one (n[-288])
and do the same

i = ln(n[-1]/n[-288])/288

From that we can calculate the APY using the formula

EAR = e**(i*n) - 1

where n = 365 days in the year, and i from our previous calculation

And convert to %