Function assignment 

pub fn assignment() -> AssignmentBuilder

Top-level constructor for an empty AssignmentBuilder.

Equivalent to AssignmentBuilder::default but reads more naturally at the call site:

use csp_solver::assignment;

let sol = assignment()
    .rows(2)
    .cols(2)
    .cost(|i, k| (i + k) as f64)
    .solve()
    .expect("trivially solvable");
assert_eq!(sol.assign.len(), 2);