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Merge pull request #712 from mir-protocol/comment_batch_opening

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Document batch opening function
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wborgeaud 2022-09-11 18:56:12 +02:00 committed by GitHub
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2 changed files with 9 additions and 1 deletions
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8
plonky2/src/fri/oracle.rs
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@ -180,7 +180,15 @@ impl<F: RichField + Extendable<D>, C: GenericConfig<D, F = F>, const D: usize>
// Final low-degree polynomial that goes into FRI. // Final low-degree polynomial that goes into FRI.
let mut final_poly = PolynomialCoeffs::empty(); let mut final_poly = PolynomialCoeffs::empty();
// Each batch `i` consists of an opening point `z_i` and polynomials `{f_ij}_j` to be opened at that point.
// For each batch, we compute the composition polynomial `F_i = sum alpha^j f_ij`,
// where `alpha` is a random challenge in the extension field.
// The final polynomial is then computed as `final_poly = sum_i alpha^(k_i) (F_i(X) - F_i(z_i))/(X-z_i)`
// where the `k_i`s are chosen such that each power of `alpha` appears only once in the final sum.
// There are usually two batches for the openings at `zeta` and `g * zeta`.
// The oracles used in Plonky2 are given in `FRI_ORACLES` in `plonky2/src/plonk/plonk_common.rs`.
for FriBatchInfo { point, polynomials } in &instance.batches { for FriBatchInfo { point, polynomials } in &instance.batches {
// Collect the coefficients of all the polynomials in `polynomials`.
let polys_coeff = polynomials.iter().map(|fri_poly| { let polys_coeff = polynomials.iter().map(|fri_poly| {
&oracles[fri_poly.oracle_index].polynomials[fri_poly.polynomial_index] &oracles[fri_poly.oracle_index].polynomials[fri_poly.polynomial_index]
}); });

2
plonky2/src/fri/structure.rs
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@ -42,7 +42,7 @@ pub struct FriBatchInfoTarget<const D: usize> {
#[derive(Copy, Clone, Debug)] #[derive(Copy, Clone, Debug)]
pub struct FriPolynomialInfo { pub struct FriPolynomialInfo {
/// Index into `FriInstanceInfoTarget`'s `oracles` list. /// Index into `FriInstanceInfo`'s `oracles` list.
pub oracle_index: usize, pub oracle_index: usize,
/// Index of the polynomial within the oracle. /// Index of the polynomial within the oracle.
pub polynomial_index: usize, pub polynomial_index: usize,