Score Types

The score represents the quality of a solution. SolverForge provides several score types with increasing granularity. Choose the simplest one that captures your constraint hierarchy.

Available Score Types

HardSoftScore (Most Common)

use solverforge::prelude::*;

// Constants for common impacts
HardSoftScore::ZERO
HardSoftScore::ONE_HARD        // 1 hard, 0 soft
HardSoftScore::ONE_SOFT        // 0 hard, 1 soft

// Custom values
HardSoftScore::of_hard(-5)
HardSoftScore::of_soft(-10)
HardSoftScore::of(-2, -15)     // -2 hard, -15 soft

Hard constraints are rules that must not be broken (e.g., “no employee works two shifts at the same time”). A solution with any hard penalty is infeasible.

Soft constraints are preferences to optimize (e.g., “prefer assigning employees to their preferred shifts”). The solver minimizes soft penalties after satisfying all hard constraints.

let score = HardSoftScore::of(-1, -50);
score.is_feasible()  // false — has hard violations

SoftScore

For problems with only preferences and no hard rules:

SoftScore::ZERO
SoftScore::ONE
SoftScore::of(-5)

HardMediumSoftScore

Three-level priority:

HardMediumSoftScore::of(-1, 0, -10)
// hard: must not violate
// medium: strongly prefer to satisfy
// soft: nice to have

HardSoftDecimalScore

Like HardSoftScore but with fixed-point decimal precision. Values are i64 internally, auto-scaled by 100,000:

HardSoftDecimalScore::ZERO
HardSoftDecimalScore::ONE_HARD    // scaled to 100,000
HardSoftDecimalScore::ONE_SOFT

HardSoftDecimalScore::of(-1, -3)          // auto-scaled: -100000, -300000
HardSoftDecimalScore::of_scaled(-150000, -370000)  // raw scaled values

BendableScore

Configurable number of hard and soft levels using const generics:

// 2 hard levels, 3 soft levels
let score = BendableScore::<2, 3>::of([-1, 0], [-5, -3, -1]);
let zero = BendableScore::<2, 3>::zero();

Use when you need more than three priority tiers.

Score Arithmetic

All score types support standard operations:

let a = HardSoftScore::of(-1, -5);
let b = HardSoftScore::of(0, -3);
let sum = a + b;           // (-1, -8)

Choosing a Score Type

1. Start with HardSoftScore — it covers most problems
2. If you need decimal precision, use HardSoftDecimalScore
3. If you have three clear priority tiers, use HardMediumSoftScore
4. If you need more tiers, use BendableScore
5. If you have no hard constraints at all, use SoftScore

See Also

• Constraint Streams — Using scores in penalize / reward
• Score Analysis — Understanding score breakdowns