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Fix matrix balancing #33

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Nov 9, 2021
Merged

Fix matrix balancing #33

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30 changes: 15 additions & 15 deletions src/ahp/constraint_systems.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -34,20 +34,20 @@ fn to_matrix_helper<F: Field>(
new_matrix
}

fn balance_matrices<F: Field>(a_matrix: &mut Matrix<F>, b_matrix: &mut Matrix<F>) {
let mut a_density: usize = a_matrix.iter().map(|row| row.len()).sum();
let mut b_density: usize = b_matrix.iter().map(|row| row.len()).sum();
let mut max_density = std::cmp::max(a_density, b_density);
let mut a_is_denser = a_density == max_density;
// TODO: write a test to check that `balance_matrices` improves the balancing of the matrices
// A and B by distributing the non-zero elements (more or less) evenly between the two.
fn balance_matrices<F: Field>(a_matrix: &mut Vec<Vec<(F, VarIndex)>>, b_matrix: &mut Vec<Vec<(F, VarIndex)>>) {
let mut a_weight: usize = a_matrix.iter().map(|row| row.len()).sum();
let mut b_weight: usize = b_matrix.iter().map(|row| row.len()).sum();
for (a_row, b_row) in a_matrix.iter_mut().zip(b_matrix) {
if a_is_denser {
let a_row_size = a_row.len();
let b_row_size = b_row.len();
let a_row_weight = a_row.len();
let b_row_weight = b_row.len();
if (a_weight < b_weight && a_row_weight < b_row_weight) ||
(a_weight > b_weight && a_row_weight > b_row_weight)
{
std::mem::swap(a_row, b_row);
a_density = a_density - a_row_size + b_row_size;
b_density = b_density - b_row_size + a_row_size;
max_density = std::cmp::max(a_density, b_density);
a_is_denser = a_density == max_density;
a_weight = a_weight - a_row_weight + b_row_weight;
b_weight = b_weight - b_row_weight + a_row_weight;
}
}
}
Expand Down Expand Up @@ -108,10 +108,10 @@ pub(crate) struct IndexerConstraintSystem<F: Field> {

impl<F: Field> IndexerConstraintSystem<F> {
pub(crate) fn process_matrices(&mut self) {
let mut a = to_matrix_helper(&self.a, self.num_input_variables);
let mut b = to_matrix_helper(&self.b, self.num_input_variables);
balance_matrices(&mut self.a, &mut self.b);
let a = to_matrix_helper(&self.a, self.num_input_variables);
let b = to_matrix_helper(&self.b, self.num_input_variables);
let c = to_matrix_helper(&self.c, self.num_input_variables);
balance_matrices(&mut a, &mut b);
self.a_matrix = Some(a);
self.b_matrix = Some(b);
self.c_matrix = Some(c);
Expand Down