OpenTally/src/constraints.rs

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/* OpenTally: Open-source election vote counting
* Copyright © 2021 Lee Yingtong Li (RunasSudo)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
use crate::election::{Candidate, CandidateState, CountCard, CountState, Election};
use crate::numbers::Number;
use crate::stv::{ConstraintMode, STVOptions};
use itertools::Itertools;
use ndarray::{Array, Dimension, IxDyn};
use std::collections::HashMap;
use std::fmt;
use std::ops;
/// Constraints for an [crate::election::Election]
#[derive(Debug)]
pub struct Constraints(pub Vec<Constraint>);
impl Constraints {
/// Parse the given CON file and return a [Constraints]
pub fn from_con<I: Iterator<Item=String>>(lines: I) -> Self {
let mut constraints = Constraints(Vec::new());
for line in lines {
let mut bits = line.split(" ").peekable();
// Read constraint category
let mut constraint_name = String::new();
let x = bits.next().expect("Syntax Error");
if x.starts_with('"') {
if x.ends_with('"') {
constraint_name.push_str(&x[1..x.len()-1]);
} else {
constraint_name.push_str(&x[1..]);
while !bits.peek().expect("Syntax Error").ends_with('"') {
constraint_name.push_str(" ");
constraint_name.push_str(bits.next().unwrap());
}
let x = bits.next().unwrap();
constraint_name.push_str(" ");
constraint_name.push_str(&x[..x.len()-1]);
}
} else {
constraint_name.push_str(x);
}
// Read constraint group
let mut group_name = String::new();
let x = bits.next().expect("Syntax Error");
if x.starts_with('"') {
if x.ends_with('"') {
group_name.push_str(&x[1..x.len()-1]);
} else {
group_name.push_str(&x[1..]);
while !bits.peek().expect("Syntax Error").ends_with('"') {
group_name.push_str(" ");
group_name.push_str(bits.next().unwrap());
}
let x = bits.next().unwrap();
group_name.push_str(" ");
group_name.push_str(&x[..x.len()-1]);
}
} else {
group_name.push_str(x);
}
// Read min, max
let min: usize = bits.next().expect("Syntax Error").parse().expect("Syntax Error");
let max: usize = bits.next().expect("Syntax Error").parse().expect("Syntax Error");
// Read candidates
let mut candidates: Vec<usize> = Vec::new();
for x in bits {
candidates.push(x.parse::<usize>().expect("Syntax Error") - 1);
}
// Insert constraint/group
let constraint = match constraints.0.iter_mut().filter(|c| c.name == constraint_name).next() {
Some(c) => { c }
None => {
let c = Constraint {
name: constraint_name,
groups: Vec::new(),
};
constraints.0.push(c);
constraints.0.last_mut().unwrap()
}
};
if constraint.groups.iter().any(|g| g.name == group_name) {
panic!("Duplicate group \"{}\" in constraint \"{}\"", group_name, constraint.name);
}
constraint.groups.push(ConstrainedGroup {
name: group_name,
candidates: candidates,
min: min,
max: max,
});
}
// TODO: Validate constraints
return constraints;
}
}
/// A single dimension of constraint
#[derive(Debug)]
pub struct Constraint {
/// Name of this constraint
pub name: String,
/// Groups of candidates within this constraint
pub groups: Vec<ConstrainedGroup>,
}
/// A group of candidates, of which a certain minimum and maximum must be elected
#[derive(Debug)]
pub struct ConstrainedGroup {
/// Name of this group
pub name: String,
/// Indexes of [crate::election::Candidate]s to constrain
pub candidates: Vec<usize>,
/// Minimum number to elect
pub min: usize,
/// Maximum number to elect
pub max: usize,
}
/// Error reaching a stable state when processing constraints
#[derive(Debug)]
pub enum ConstraintError {
/// No conformant result is possible
NoConformantResult,
}
/// Cell in a [ConstraintMatrix]
#[derive(Clone)]
pub struct ConstraintMatrixCell {
/// Number of elected candidates in this cell
pub elected: usize,
/// Minimum number of candidates which must be elected from this cell for a conformant result
pub min: usize,
/// Maximum number of candidates which may be elected from this cell for a conformant result
pub max: usize,
/// Total number of elected or hopeful candidates in this cell
pub cands: usize,
}
/// Hypercube/tensor of [ConstraintMatrixCell]s representing the conformant combinations of elected candidates
pub struct ConstraintMatrix(pub Array<ConstraintMatrixCell, IxDyn>);
impl ConstraintMatrix {
/// Return a new [ConstraintMatrix], with the specified number of groups for each constraint dimension
pub fn new(constraints: &mut [usize]) -> Self {
// Add 1 to dimensions for totals cells
for c in constraints.iter_mut() {
*c += 1;
}
return Self(Array::from_elem(
IxDyn(constraints),
ConstraintMatrixCell {
elected: 0,
min: 0,
max: 0,
cands: 0,
}
));
}
/// Initialise the matrix once the number of candidates in each innermost cell, and min/max for each constraint group, have been specified
pub fn init(&mut self) {
// Compute candidate totals
self.recount_cands();
// Initialise max for grand total cell
let idx = IxDyn(&vec![0; self.0.ndim()][..]);
self.0[&idx].max = self.0[&idx].cands;
// Initialise max for inner cells (>=2 zeroes)
for idx in ndarray::indices(self.0.shape()) {
if (0..idx.ndim()).fold(0, |acc, d| if idx[d] != 0 { acc + 1 } else { acc }) < 2 {
continue;
}
self.0[&idx].max = self.0[&idx].cands;
}
// NB: Bounds on min, max, etc. will be further refined in initial step() calls
}
/// Update cands/elected in innermost cells based on the provided [CountState::candidates](crate::election::CountState::candidates)
pub fn update_from_state<N: Number>(&mut self, election: &Election<N>, candidates: &HashMap<&Candidate, CountCard<N>>) {
let constraints = election.constraints.as_ref().unwrap();
// Reset innermost cells
for idx in ndarray::indices(self.0.shape()) {
if (0..idx.ndim()).fold(0, |acc, d| if idx[d] == 0 { acc + 1 } else { acc }) != 0 {
continue;
}
self.0[&idx].cands = 0;
self.0[&idx].elected = 0;
}
for (i, candidate) in election.candidates.iter().enumerate() {
let idx: Vec<usize> = constraints.0.iter().map(|c| {
for (j, group) in c.groups.iter().enumerate() {
if group.candidates.contains(&i) {
return j + 1;
}
}
panic!("Candidate \"{}\" not represented in constraint \"{}\"", candidate.name, c.name);
}).collect();
let cell = &mut self[&idx[..]];
let count_card = candidates.get(candidate).unwrap();
match count_card.state {
CandidateState::Hopeful | CandidateState::Guarded => {
cell.cands += 1;
}
CandidateState::Elected => {
cell.cands += 1;
cell.elected += 1;
}
CandidateState::Withdrawn | CandidateState::Doomed | CandidateState::Excluded => {}
}
}
}
/// Recompute [cands](ConstraintMatrixCell::cands) and [elected](ConstraintMatrixCell::elected) for totals cells based on the innermost cells
pub fn recount_cands(&mut self) {
let shape = Vec::from(self.0.shape());
// Compute cands/elected totals
for nzeroes in 1..self.0.ndim()+1 {
for idx in ndarray::indices(self.0.shape()) {
// First compute totals cells with 1 zero, then 2 zeroes, ... then grand total (all zeroes)
if (0..idx.ndim()).fold(0, |acc, d| if idx[d] == 0 { acc + 1 } else { acc }) != nzeroes {
continue;
}
self.0[&idx].cands = 0;
self.0[&idx].elected = 0;
// The axis along which to sum - if multiple, just pick the first, as these should agree
let zero_axis = (0..idx.ndim()).filter(|d| idx[*d] == 0).next().unwrap();
// Traverse along the axis and sum the candidates
let mut idx2 = idx.clone();
for coord in 1..shape[zero_axis] {
idx2[zero_axis] = coord;
self.0[&idx].cands += self.0[&idx2].cands;
self.0[&idx].elected += self.0[&idx2].elected;
}
}
}
}
/// Attempt to advance the matrix one step towards a stable state
///
/// Returns `Ok(true)` if in a stable state, `Ok(false)` if not, and `ConstraintError` on an error.
///
pub fn step(&mut self) -> Result<bool, ConstraintError> {
let shape = Vec::from(self.0.shape());
for idx in ndarray::indices(self.0.shape()) {
let cell = &mut self.0[&idx];
// Rule 1: Ensure elected < min < max < cands
if cell.min < cell.elected {
cell.min = cell.elected;
return Ok(false);
}
if cell.max > cell.cands {
cell.max = cell.cands;
return Ok(false);
}
if cell.min > cell.max {
return Err(ConstraintError::NoConformantResult);
}
let nzeroes = (0..idx.ndim()).fold(0, |acc, d| if idx[d] == 0 { acc + 1 } else { acc });
// Rule 2/3: Ensure min/max is possible in innermost cells
if nzeroes == 0 {
for axis in 0..self.0.ndim() {
let mut idx2 = idx.clone();
// What is the min/max number of candidates that can be elected from other cells in this axis?
let (other_max, other_min) = (1..shape[axis]).fold((0, 0), |(acc_max, acc_min), coord| {
if coord == idx[axis] {
return (acc_max, acc_min);
}
idx2[axis] = coord;
return (acc_max + self.0[&idx2].max, acc_min + self.0[&idx2].min);
});
// What is the min/max number of candidates that can be elected along this axis?
idx2[axis] = 0;
let axis_max = self.0[&idx2].max;
let axis_min = self.0[&idx2].min;
// How many must be elected from this cell?
let this_max = (axis_max as i32) - (other_min as i32);
let this_min = (axis_min as i32) - (other_max as i32);
if this_max < (self.0[&idx].max as i32) {
self.0[&idx].max = this_max as usize;
return Ok(false);
}
if this_min > (self.0[&idx].min as i32) {
self.0[&idx].min = this_min as usize;
return Ok(false);
}
}
}
// Rule 4/5: Ensure min/max is possible in totals cells
if nzeroes > 0 {
for axis in 0..self.0.ndim() {
if idx[axis] != 0 {
continue;
}
// What is the total min/max along this axis?
let mut idx2 = idx.clone();
let (axis_max, axis_min) = (1..shape[axis]).fold((0, 0), |(acc_max, acc_min), coord| {
idx2[axis] = coord;
return (acc_max + self.0[&idx2].max, acc_min + self.0[&idx2].min);
});
if axis_max < self.0[&idx].max {
self.0[&idx].max = axis_max;
return Ok(false);
}
if axis_min > self.0[&idx].min {
self.0[&idx].min = axis_min;
return Ok(false);
}
}
}
}
return Ok(true);
}
}
impl fmt::Display for ConstraintMatrix {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> std::fmt::Result {
let shape = self.0.shape();
let mut result = String::new();
// TODO: >2 dimensions
if shape.len() == 1 {
result.push_str("+");
for _ in 0..shape[0] {
result.push_str("-------------+");
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Elected: {:2}", self[&[x]].elected));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Min: {:2}", self[&[x]].min));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Max: {:2}", self[&[x]].max));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Cands: {:2}", self[&[x]].cands));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("+");
for _ in 0..shape[0] {
result.push_str("-------------+");
}
result.push_str("\n");
} else if shape.len() == 2 {
for y in 0..shape[1] {
result.push_str("+");
for _ in 0..shape[0] {
result.push_str(if y == 1 { "=============+" } else { "-------------+" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Elected: {:2}", self[&[x, y]].elected));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Min: {:2}", self[&[x, y]].min));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Max: {:2}", self[&[x, y]].max));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
result.push_str("|");
for x in 0..shape[0] {
result.push_str(&format!(" Cands: {:2}", self[&[x, y]].cands));
result.push_str(if x == 0 { "" } else { " |" });
}
result.push_str("\n");
}
result.push_str("+");
for _ in 0..shape[0] {
result.push_str("-------------+");
}
result.push_str("\n");
} else {
todo!();
}
return f.write_str(&result);
}
}
impl ops::Index<&[usize]> for ConstraintMatrix {
type Output = ConstraintMatrixCell;
fn index(&self, index: &[usize]) -> &Self::Output { &self.0[index] }
}
impl ops::IndexMut<&[usize]> for ConstraintMatrix {
fn index_mut(&mut self, index: &[usize]) -> &mut Self::Output { &mut self.0[index] }
}
/// Return the [Candidate]s referred to in the given [ConstraintMatrixCell] at location `idx`
fn candidates_in_constraint_cell<'a, N: Number>(election: &'a Election<N>, candidates: &HashMap<&Candidate, CountCard<N>>, idx: &[usize]) -> Vec<&'a Candidate> {
let mut result: Vec<&Candidate> = Vec::new();
for (i, candidate) in election.candidates.iter().enumerate() {
let cc = candidates.get(candidate).unwrap();
if cc.state != CandidateState::Hopeful {
continue;
}
// Is this candidate within this constraint cell?
let mut matches = true;
for (coord, constraint) in idx.iter().zip(election.constraints.as_ref().unwrap().0.iter()) {
let group = &constraint.groups[coord - 1]; // The group referred to by this constraint cell
if !group.candidates.contains(&i) {
matches = false;
break;
}
}
if matches {
result.push(candidate);
}
}
return result;
}
/// Update the constraints matrix, and perform the necessary actions given by [STVOptions::constraint_mode]
pub fn update_constraints<N: Number>(state: &mut CountState<N>, opts: &STVOptions) -> bool {
if state.constraint_matrix.is_none() {
return false;
}
let cm = state.constraint_matrix.as_mut().unwrap();
// Update cands/elected
cm.update_from_state(&state.election, &state.candidates);
cm.recount_cands();
// Iterate for stable state
//println!("{}", cm);
while !cm.step().expect("No conformant result is possible") {
//println!("{}", cm);
}
//println!("{}", cm);
match opts.constraint_mode {
ConstraintMode::GuardDoom => {
// Check for guarded or doomed candidates
let mut guarded_or_doomed = false;
for idx in ndarray::indices(cm.0.shape()) {
if (0..idx.ndim()).fold(0, |acc, d| if idx[d] == 0 { acc + 1 } else { acc }) != 0 {
continue;
}
let cell = &cm.0[&idx];
if cell.elected == cell.max {
// Doom remaining candidates in this cell
let doomed = candidates_in_constraint_cell(state.election, &state.candidates, idx.slice());
if !doomed.is_empty() {
for candidate in doomed.iter() {
state.candidates.get_mut(candidate).unwrap().state = CandidateState::Doomed;
}
state.logger.log_smart(
"{} must be doomed to comply with constraints.",
"{} must be doomed to comply with constraints.",
doomed.iter().map(|c| c.name.as_str()).sorted().collect()
);
guarded_or_doomed = true;
}
}
if cell.cands == cell.min {
// Guard remaining candidates in this cell
let guarded = candidates_in_constraint_cell(state.election, &state.candidates, idx.slice());
if !guarded.is_empty() {
for candidate in guarded.iter() {
state.candidates.get_mut(candidate).unwrap().state = CandidateState::Guarded;
}
state.logger.log_smart(
"{} must be guarded to comply with constraints.",
"{} must be guarded to comply with constraints.",
guarded.iter().map(|c| c.name.as_str()).sorted().collect()
);
guarded_or_doomed = true;
}
}
}
return guarded_or_doomed;
}
_ => { todo!() }
}
//return false;
}
#[cfg(test)]
mod tests {
use super::*;
fn assert_cell(cm: &ConstraintMatrix, idx: &[usize], elected: usize, min: usize, max: usize, cands: usize) {
assert_eq!(cm[idx].elected, elected, "Failed to validate elected at {:?}", idx);
assert_eq!(cm[idx].min, min, "Failed to validate min at {:?}", idx);
assert_eq!(cm[idx].max, max, "Failed to validate min at {:?}", idx);
assert_eq!(cm[idx].cands, cands, "Failed to validate cands at {:?}", idx);
}
#[test]
fn cm_otten() {
let mut cm = ConstraintMatrix::new(&mut [3, 2]);
// Totals
let c = &mut cm[&[0, 1]]; c.min = 7; c.max = 7;
let c = &mut cm[&[0, 2]]; c.min = 7; c.max = 7;
let c = &mut cm[&[1, 0]]; c.min = 7; c.max = 7;
let c = &mut cm[&[2, 0]]; c.min = 6; c.max = 6;
let c = &mut cm[&[3, 0]]; c.min = 1; c.max = 1;
// Candidates
let c = &mut cm[&[1, 1]]; c.cands = 4;
let c = &mut cm[&[2, 1]]; c.cands = 11;
let c = &mut cm[&[3, 1]]; c.cands = 2;
let c = &mut cm[&[1, 2]]; c.cands = 7;
let c = &mut cm[&[2, 2]]; c.cands = 3;
let c = &mut cm[&[3, 2]]; c.cands = 1;
// Init
cm.init();
while !cm.step().expect("No conformant result") {}
println!("{}", cm);
assert_cell(&cm, &[1, 1], 0, 0, 4, 4);
assert_cell(&cm, &[2, 1], 0, 3, 6, 11);
assert_cell(&cm, &[3, 1], 0, 0, 1, 2);
assert_cell(&cm, &[0, 1], 0, 7, 7, 17);
assert_cell(&cm, &[1, 2], 0, 3, 7, 7);
assert_cell(&cm, &[2, 2], 0, 0, 3, 3);
assert_cell(&cm, &[3, 2], 0, 0, 1, 1);
assert_cell(&cm, &[0, 2], 0, 7, 7, 11);
assert_cell(&cm, &[1, 0], 0, 7, 7, 11);
assert_cell(&cm, &[2, 0], 0, 6, 6, 14);
assert_cell(&cm, &[3, 0], 0, 1, 1, 3);
assert_cell(&cm, &[0, 0], 0, 14, 14, 28);
// Election of Welsh man
cm[&[3, 1]].elected += 1;
cm.recount_cands();
while !cm.step().expect("No conformant result") {}
println!("{}", cm);
assert_cell(&cm, &[1, 1], 0, 0, 3, 4);
assert_cell(&cm, &[2, 1], 0, 3, 6, 11);
assert_cell(&cm, &[3, 1], 1, 1, 1, 2);
assert_cell(&cm, &[0, 1], 1, 7, 7, 17); // Error in Otten paper
assert_cell(&cm, &[1, 2], 0, 4, 7, 7);
assert_cell(&cm, &[2, 2], 0, 0, 3, 3);
assert_cell(&cm, &[3, 2], 0, 0, 0, 1);
assert_cell(&cm, &[0, 2], 0, 7, 7, 11);
assert_cell(&cm, &[1, 0], 0, 7, 7, 11);
assert_cell(&cm, &[2, 0], 0, 6, 6, 14);
assert_cell(&cm, &[3, 0], 1, 1, 1, 3);
assert_cell(&cm, &[0, 0], 1, 14, 14, 28);
// Remaining Welsh man, Welsh woman doomed
cm[&[3, 1]].cands -= 1;
cm[&[3, 2]].cands -= 1;
// Election of 2 English men, 2 English women
// Exclusion of 1 Scottish woman
cm[&[1, 1]].elected += 2;
cm[&[1, 2]].elected += 2;
cm[&[2, 2]].cands -= 1;
cm.recount_cands();
while !cm.step().expect("No conformant result") {}
println!("{}", cm);
assert_cell(&cm, &[1, 1], 2, 2, 2, 4);
assert_cell(&cm, &[2, 1], 0, 4, 4, 11);
assert_cell(&cm, &[3, 1], 1, 1, 1, 1);
assert_cell(&cm, &[0, 1], 3, 7, 7, 16); // Error in Otten paper
assert_cell(&cm, &[1, 2], 2, 5, 5, 7);
assert_cell(&cm, &[2, 2], 0, 2, 2, 2);
assert_cell(&cm, &[3, 2], 0, 0, 0, 0);
assert_cell(&cm, &[0, 2], 2, 7, 7, 9);
assert_cell(&cm, &[1, 0], 4, 7, 7, 11);
assert_cell(&cm, &[2, 0], 0, 6, 6, 13);
assert_cell(&cm, &[3, 0], 1, 1, 1, 1);
assert_cell(&cm, &[0, 0], 5, 14, 14, 25);
}
}