In-Step Range

InStepRangeFunction returns the greatest grid point not exceeding the upper expression:

$$y=lb+\lfloor \frac{ub-lb}{step}\rfloor step.$$

It is a numeric stepping function, not a Boolean membership test. step must be finite and strictly positive, and the implementation rejects ub < lb when the value is evaluated or constrained.

Solver mathematical model

Let $d=ub-lb$, $k=\lfloor d/step\rfloor$, and $y=lb+stepk$. The solver receives the delegated floor encoding for $k$, together with the explicit ordering row

$$ub-lb\ge 0.$$

The quotient is divided by step before flooring; therefore a range from 1 to 10 with step 3 returns 10, while a range from 1 to 9 returns 7.

Kotlin API

val stepped = InStepRangeFunction(
    lb = lower,
    ub = upper,
    step = Flt64(3.0),
    converter = IntoValue.Identity,
    name = "stepped"
)

Rust API

Rust now exposes the same numeric function:

let stepped = InStepRangeFunction::new(
    1, "stepped", lower, upper, 3.0_f64,
);

The former grid-membership function is explicitly named InStepRangeIndicatorFunction; use it when the required result is a binary “is this value one of the grid points?” flag.

Kotlin/Rust example

Kotlin

val stepped = InStepRangeFunction(
    lb = LinearPolynomial(emptyList(), Flt64(1.0)),
    ub = LinearPolynomial(emptyList(), Flt64(10.0)),
    step = Flt64(3.0),
    converter = IntoValue.Identity,
    name = "stepped"
)
check(stepped.evaluate(emptyMap()) == Flt64(10.0))

Rust

let stepped = InStepRangeFunction::new(1, "stepped", lower, upper, 3.0_f64);
assert_eq!(stepped.calculate_value(&tokens, false), Some(10.0));

Tests and references

• Kotlin numeric focused test: InStepRangeFunctionDedicatedTest.kt
• Kotlin membership focused test: InStepRangeIndicatorFunctionDedicatedTest.kt
• Kotlin implementation: InStepRange.kt
• Rust numeric implementation: in_step_range.rs
• Rust numeric focused test: function_symbol_in_step_range.rs
• Rust membership focused test: function_symbol_in_step_range_indicator.rs

The focused tests assert the numeric function's two Floor helpers and four registered rows, and the indicator's seven helpers and sixteen point/OR rows; they also cover grid boundaries, missing input, and invalid step/Big-M values.

The endpoint function has no unused Big-M parameter because FloorFunction does not use one. InStepRangeIndicatorFunction is available in both Kotlin and Rust for membership tests and uses the shared 1e-10 boundary epsilon. Kotlin accepts an optional bigM constructor argument; Rust uses InStepRangeIndicatorFunction::with_big_m when an explicit positive finite value is required, and new otherwise follows the token-derived/default policy.