Struct coin_cbc::Solution

pub struct Solution { /* private fields */ }

A solution to a MILP problem.

This is a thin wrapper over a raw::Model with accessors using the typed identifiers.

Implementations

impl Solution

pub fn raw(&self) -> &Model

Gets a shared reference to the internal raw::Model.

Examples found in repository

examples/knapsack.rs (line 50)

fn main() {
    // a simple knapsack problem
    // Maximize  5x[1] + 3x[2] + 2x[3] + 7x[4] + 4x[5]
    // s.t.      2x[1] + 8x[2] + 4x[3] + 2x[4] + 5x[5] <= 10
    // All x binary

    // Create the problem.
    let mut m = Model::default();

    // The columns. m.add_binary() returns a typed indentifier for a
    // column.
    let cols = [
        m.add_binary(),
        m.add_binary(),
        m.add_binary(),
        m.add_binary(),
        m.add_binary(),
    ];

    // The row. m.add_row() returns a typed identifier for a row.
    let row = m.add_row();

    // Set the bound of the knapsack constraint.
    m.set_row_upper(row, 10.);

    // Set weights of the constraint.
    m.set_weight(row, cols[0], 2.);
    m.set_weight(row, cols[1], 8.);
    m.set_weight(row, cols[2], 4.);
    m.set_weight(row, cols[3], 2.);
    m.set_weight(row, cols[4], 5.);

    // Set objective coefficients
    m.set_obj_coeff(cols[0], 5.);
    m.set_obj_coeff(cols[1], 3.);
    m.set_obj_coeff(cols[2], 2.);
    m.set_obj_coeff(cols[3], 7.);
    m.set_obj_coeff(cols[4], 4.);

    // Set objective sense.
    m.set_obj_sense(Sense::Maximize);

    // Solve the problem. Returns the solution
    let sol = m.solve();

    // Check the result. sol.raw() returns a shared reference to the
    // raw bindings, allowing to use all getters.
    assert_eq!(Status::Finished, sol.raw().status());
    assert_eq!(16., sol.raw().obj_value());

    // Check for the solution.
    assert_eq!(1., sol.col(cols[0]));
    assert_eq!(0., sol.col(cols[1]));
    assert_eq!(0., sol.col(cols[2]));
    assert_eq!(1., sol.col(cols[3]));
    assert_eq!(1., sol.col(cols[4]));
}

pub fn into_raw(self) -> Model

Gets the internal raw::Model

pub fn col(&self, col: Col) -> f64

Gets the value of the given column in the solution.

Examples found in repository

examples/knapsack.rs (line 54)

fn main() {
    // a simple knapsack problem
    // Maximize  5x[1] + 3x[2] + 2x[3] + 7x[4] + 4x[5]
    // s.t.      2x[1] + 8x[2] + 4x[3] + 2x[4] + 5x[5] <= 10
    // All x binary

    // Create the problem.
    let mut m = Model::default();

    // The columns. m.add_binary() returns a typed indentifier for a
    // column.
    let cols = [
        m.add_binary(),
        m.add_binary(),
        m.add_binary(),
        m.add_binary(),
        m.add_binary(),
    ];

    // The row. m.add_row() returns a typed identifier for a row.
    let row = m.add_row();

    // Set the bound of the knapsack constraint.
    m.set_row_upper(row, 10.);

    // Set weights of the constraint.
    m.set_weight(row, cols[0], 2.);
    m.set_weight(row, cols[1], 8.);
    m.set_weight(row, cols[2], 4.);
    m.set_weight(row, cols[3], 2.);
    m.set_weight(row, cols[4], 5.);

    // Set objective coefficients
    m.set_obj_coeff(cols[0], 5.);
    m.set_obj_coeff(cols[1], 3.);
    m.set_obj_coeff(cols[2], 2.);
    m.set_obj_coeff(cols[3], 7.);
    m.set_obj_coeff(cols[4], 4.);

    // Set objective sense.
    m.set_obj_sense(Sense::Maximize);

    // Solve the problem. Returns the solution
    let sol = m.solve();

    // Check the result. sol.raw() returns a shared reference to the
    // raw bindings, allowing to use all getters.
    assert_eq!(Status::Finished, sol.raw().status());
    assert_eq!(16., sol.raw().obj_value());

    // Check for the solution.
    assert_eq!(1., sol.col(cols[0]));
    assert_eq!(0., sol.col(cols[1]));
    assert_eq!(0., sol.col(cols[2]));
    assert_eq!(1., sol.col(cols[3]));
    assert_eq!(1., sol.col(cols[4]));
}

pub fn is_basic(&self, col: Col) -> bool

Returns whether the given variable is basic (equal to zero in the solution)

pub fn row_activity(&self, row: Row) -> f64

Available on crate feature cbc-310 only.

Primal row solution : gets the value of the linear expression in the given constraint

pub fn reduced_cost(&self, col: Col) -> f64

Available on crate feature cbc-310 only.

For a minimization problem, the reduced cost of a nonbasic variable (a variable that is null in the solution) is the amount by which the value of the objective will decrease if we increase the value of the variable by 1