BPT Oracle

As of now, the Oracle documentation is only available in english.
To price LP tokens, it is not enough to simply add the values of all assets in the pool as this is easily manipulated. We use a more robust procedure for calculating Balancer LP token values.
For a given Balancer pool containing assets 1, ..., n, define the following:
wi=weight of asset iri=amount (in # tokens) of asset ipi=price of asset iS=total # BPT tokensw_i = \text{weight of asset } i \\
r_i = \text{amount (in \# tokens) of asset } i \\
p_i = \text{price of asset } i \\
S = \text{total \# BPT tokens}

wi​=weight of asset iri​=amount (in # tokens) of asset ipi​=price of asset iS=total # BPT tokens
The constant product of the Balancer pool is
k=∏i=1nriwik = \prod_{i=1}^{n} r_i^{w_i}k=i=1∏n​riwi​​
Note that the amounts rir_iri​
are easily manipulatable, but the product kkk
is not. And, as we require asset pricing oracles elsewhere, we can presume that the prices pip_ipi​
are also not easily manipulatable (controls to assure against this will be discussed elsewhere).
To make the manipulation-resistant BPT oracles, it will be enough to express the pricing of BPT tokens in terms of solely manipulation-resistant variables wi,pi,k,Sw_i, p_i, k, Swi​,pi​,k,S
.
The portfolio value of the Balancer pool can be calculated as
BPT total value=k∏i=1n(piwi)wi\text{BPT total value} = k \prod_{i=1}^n \left( \frac{p_i}{w_i} \right)^{w_i}BPT total value=ki=1∏n​(wi​pi​​)wi​
Then, in turn, the BPT price can be calculated as
pBPT=BPT total valueS=k∏i=1n(piwi)wiSp_{BPT} = \frac{\text{BPT total value}}{S} = \frac{k \prod_{i=1}^n \left( \frac{p_i}{w_i} \right)^{w_i}
}{S}pBPT​=SBPT total value​=Sk∏i=1n​(wi​pi​​)wi​​

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