Struct AssignmentBuilder 

pub struct AssignmentBuilder { /* private fields */ }

Fluent builder for bipartite assignment COPs.

Construct via assignment() (preferred) or Default::default. All setters consume self and return self, allowing chained configuration. The terminal AssignmentBuilder::solve call validates the configuration, materializes the underlying Csp<CostFiniteDomain>, runs branch-and-bound, and returns an AssignmentSolution (or an AssignmentError on mis-configuration / infeasibility).

Implementations

impl AssignmentBuilder

pub fn rows(self, n: usize) -> Self

Set the number of source rows.

pub fn cols(self, n: usize) -> Self

Set the number of target columns.

pub fn cost(self, f: impl Fn(usize, usize) -> f64) -> Self

Eagerly populate the row-major cost matrix.

Calls f(i, k) exactly once per (row, col) cell during this method, stores the result in an internal Vec<f64>, and returns self. No closure is retained, which keeps the builder Send + Sync even when constructed from non-'static captures.

Panics

Panics if AssignmentBuilder::rows or AssignmentBuilder::cols has not been called yet — both dimensions are required to know how to walk f.

pub fn row_group(self, f: impl Fn(usize) -> u8) -> Self

Tag each row with a u8 group identifier.

Rows in different groups are placed in independent AllDifferentExcept scopes, and a row may only be assigned to a column whose group identifier matches. Omitting the call (or supplying |_| 0) puts every row in a single group, which is the standard bipartite-assignment shape.

pub fn col_group(self, f: impl Fn(usize) -> u8) -> Self

Tag each column with a u8 group identifier.

See AssignmentBuilder::row_group for the semantics.

pub fn pin(self, row: usize, col: i32) -> Self

Hard-pin row row to column col.

col may be SENTINEL to force the row unmatched. Multiple pins are accumulated; conflicting pins on the same row are detected at AssignmentBuilder::solve time as AssignmentError::Infeasible.

pub fn unmatch_penalty(self, penalty: f64) -> Self

Set the per-row cost paid when a row is assigned to SENTINEL (left unmatched).

pub fn node_budget(self, budget: Option<u64>) -> Self

Override the underlying branch-and-bound node budget.

Passing None here is not the same as never calling this method: None requests an unbounded search, while the default (no call) installs a 1_000_000 node guard so a pathological problem cannot hang the caller. See crate::SolveConfig::node_budget.

pub fn solve(self) -> Result<AssignmentSolution, AssignmentError>

Validate the configuration and solve for the minimum-cost assignment.

A group-free, pin-free instance is dispatched to the closed-form Kuhn-Munkres LAP solver (always optimal, microsecond-scale, never budget-blows). Grouped or pinned instances fall through to the general branch-and-bound CSP path. See the module docs for the n≈15–18 B&B ceiling; use solve_branch_and_bound to force the CSP path on any shape.

pub fn solve_branch_and_bound( self, ) -> Result<AssignmentSolution, AssignmentError>

Force the branch-and-bound CSP path regardless of shape, bypassing the closed-form LAP dispatch in solve.

Exists for benchmarking the general solver and for the node-count invariance gate — a group-free/pin-free instance solved here exercises the exact same B&B trajectory it did before the LAP dispatch landed, so its nodes_explored / backtracks counts are a stable regression tripwire. Prefer solve in production.

Trait Implementations

impl Debug for AssignmentBuilder

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for AssignmentBuilder

fn default() -> AssignmentBuilder

Returns the “default value” for a type.