gridcraft/crates/engine/src/cmd/solver/problem.rs

use super::lp::{Row, Sense};
use super::model::{Model, Rel, Rhs};
use super::{CellRef, Trial, Value};

/// The values the solvers see at a point: the objective and `lhs − rhs` per row.
#[derive(Clone, Debug)]
pub(super) struct Point {
    pub(super) f: f64,
    pub(super) g: Vec<f64>,
}

pub(super) struct Evaluator {
    pub(super) trial: Trial,
    pub(super) sheet: usize,
    pub(super) vars: Vec<CellRef>,
    pub(super) objective: CellRef,
    pub(super) rows: Vec<Row>,
    pub(super) evals: u64,
    pub(super) budget: u64,
    /// The Limits report: the objective is this variable itself.
    pub(super) target: Option<usize>,
}

pub(super) fn as_num(v: &Value) -> f64 {
    match v {
        Value::Number(n) => *n,
        Value::Empty => 0.0,
        Value::Bool(b) => f64::from(u8::from(*b)),
        _ => f64::NAN,
    }
}

impl Evaluator {
    pub(super) fn exhausted(&self) -> bool {
        self.evals >= self.budget
    }

    /// Evaluates the model at `x`; `None` once the budget is spent.
    pub(super) fn eval(&mut self, x: &[f64]) -> Option<Point> {
        if self.exhausted() {
            return None;
        }
        self.evals += 1;
        let sets: Vec<(usize, CellRef, Value)> = self.vars.iter().zip(x).map(|(c, v)| (self.sheet, *c, Value::number(*v))).collect();
        let mut reads = Vec::with_capacity(1 + 2 * self.rows.len());
        reads.push((self.sheet, self.objective));
        for r in &self.rows {
            reads.push((self.sheet, r.lhs));
            if let Some(c) = r.rhs {
                reads.push((self.sheet, c));
            }
        }
        let vals = self.trial.run(&sets, &reads);
        let mut it = vals.iter().map(as_num);
        let f = it.next().unwrap_or(f64::NAN);
        let f = match self.target {
            Some(j) => x.get(j).copied().unwrap_or(f64::NAN),
            None => f,
        };
        let mut g = Vec::with_capacity(self.rows.len());
        for r in &self.rows {
            let l = it.next().unwrap_or(f64::NAN);
            let rv = if r.rhs.is_some() { it.next().unwrap_or(f64::NAN) } else { r.rhs_const };
            g.push(l - rv);
        }
        Some(Point { f, g })
    }
}

// ---------------------------------------------------------------- problem

pub(super) struct Problem {
    pub(super) lo: Vec<f64>,
    pub(super) hi: Vec<f64>,
    pub(super) integer: Vec<bool>,
    pub(super) rows: Vec<Row>,
}

/// Splits the constraints into variable bounds and general rows.
pub(super) fn build_problem(m: &Model) -> Problem {
    let n = m.vars.len();
    let mut lo = vec![f64::NEG_INFINITY; n];
    let mut hi = vec![f64::INFINITY; n];
    let mut has_lower = vec![false; n];
    let mut integer = vec![false; n];
    let mut rows = Vec::new();
    let var_index = |c: &CellRef| m.vars.iter().position(|v| v == c);
    for c in &m.cons {
        for (k, cell) in c.lhs.iter().enumerate() {
            let j = var_index(cell);
            match c.rel {
                Rel::Int | Rel::Bin => {
                    if let Some(j) = j {
                        if let Some(b) = integer.get_mut(j) {
                            *b = true;
                        }
                        if c.rel == Rel::Bin
                            && let (Some(l), Some(h), Some(hl)) = (lo.get_mut(j), hi.get_mut(j), has_lower.get_mut(j))
                        {
                            *l = l.max(0.0);
                            *h = h.min(1.0);
                            *hl = true;
                        }
                    }
                }
                rel => {
                    let sense = match rel {
                        Rel::Le => Sense::Le,
                        Rel::Ge => Sense::Ge,
                        _ => Sense::Eq,
                    };
                    let (rhs, rhs_const) = match &c.rhs {
                        Rhs::Const(v) => (None, *v),
                        Rhs::Cells(cells) => (cells.get(k).or_else(|| cells.first()).copied(), 0.0),
                        Rhs::None => (None, 0.0),
                    };
                    match (j, rhs) {
                        // A constant bound on a variable cell is a box bound.
                        (Some(j), None) => {
                            if let (Some(l), Some(h), Some(hl)) = (lo.get_mut(j), hi.get_mut(j), has_lower.get_mut(j)) {
                                if sense != Sense::Ge {
                                    *h = h.min(rhs_const);
                                }
                                if sense != Sense::Le {
                                    *l = l.max(rhs_const);
                                    *hl = true;
                                }
                            }
                        }
                        _ => rows.push(Row { lhs: *cell, sense, rhs, rhs_const }),
                    }
                }
            }
        }
    }
    if m.non_negative {
        for (l, hl) in lo.iter_mut().zip(&has_lower) {
            if !hl {
                *l = l.max(0.0);
            }
        }
    }
    Problem { lo, hi, integer, rows }
}