📖 Glossary

Active parameter A parameter that is included in the solver invocation for a given configuration. Conditional parameters are only active when their parent parameter has the required value; inactive parameters are omitted from the command line entirely.

Adaptive capping (see also: pruning, capped score, gated round) Early stopping once a candidate has spent the whole budget beating the incumbent allows: partial_sum > bound_multiplier × incumbent_score × n_instances. Costs never go down, so this proves the final score exceeds the bound — capping never discards a configuration that would have been accepted. Controlled by the pruning and bound_multiplier scenario fields.

Capped score The value a capped evaluation yields: a mean over only the instances that finished before the cap fired. Those are the fastest, so it understates the true score — it is a lower bound, not a measurement. Logged with a leading > and the count it covers, >2.698475 (312/473). Two capped scores cover different, differently biased prefixes and must not be compared to each other.

Configuration A complete assignment of values to all parameters in the parameter space. Also called a strategy in the context of solver portfolios. Represented internally as {name → value} string maps.

Conditional parameter A parameter whose domain is only meaningful when a parent parameter has a specific value. Declared in the .params file as child {…} [default] | parent in {val}. Conditional parameters that are inactive are omitted from the solver command line.

Cutoff time (cutoff_time) The per-run time limit in seconds passed to the target algorithm. The solver wrapper is expected to respect this limit and report TIMEOUT if reached. Adaptive capping uses this as the ceiling for individual run runtimes.

Dominance (FocusedILS) In the current implementation, configuration θ₁ dominates θ₂ when it has been evaluated at at least the same fidelity and has a strictly lower aggregate score. Ties do not count as improvements — this is what lets the fidelity grow when the incumbent survives a tie instead of being replaced endlessly by equal-scoring challengers.

The acceptance criterion is the one exception: it resolves ties in favour of the challenger, so the ILS home base can cross plateaus and drift away from a basin it cannot improve on while the incumbent stays put. ParamILS spells the two variants dominates(θ₁, θ₂, equalIsBetter).

Home base (ILS) The local optimum the next perturbation starts from — ParamILS’s last_ils_state. Distinct from the incumbent: the incumbent is the best configuration found, the home base is where the search currently is. It is replaced by the new local optimum whenever that one is at least as good, and, like the incumbent, is re-measured whenever the fidelity grows. Replacements are logged as ils: new home base: with the parameter diff against the previous one. Only the home base is perturbed, so a home base that stops moving turns the ILS into repeated random restarts from a fixed ball however the incumbent behaves — which is what the log lets you check.

Fidelity The number of leading training instances used to score each configuration. FocusedILS starts at initial_fidelity and grows by fidelity_step when the incumbent survives a challenge. Instances are taken in list order and are not shuffled.

Forbidden combination A joint assignment of parameter values that is excluded from the search. Declared in the .params file as {param1=val1, param2=val2}. Any configuration containing a forbidden combination is skipped during neighbourhood exploration.

Gated round A round whose starting configuration was capped and which then accepted no move: every neighbour that did not finish under the bound was invisible, so the round produced no search at all. Counted in the end-of-run ils: summary line. The rate differs sharply between a small perturbation and a fresh random draw, so it belongs beside any comparison of two approaches.

Incumbent The best configuration found so far during the ILS run. Updated whenever a new configuration has a strictly lower aggregate score at the required fidelity. The final incumbent is returned as the result.

Instance A benchmark problem on which the target algorithm is evaluated. Passed as a file path to the solver wrapper. RamParILS evaluates configurations across the training instance set to estimate generalisation performance.

Iterated Local Search (ILS) The search algorithm at the core of RamParILS. Alternates between local search (greedy improvement within the neighbourhood) and perturbation (random escape from a local optimum). See Algorithm for a full description.

Local optimum A configuration whose entire neighbourhood contains no strictly better configuration. ILS escapes local optima via perturbation rather than accepting them as the final answer.

Neighbourhood The set of all configurations that differ from the current configuration in exactly one parameter value. Local search explores the neighbourhood at each step, evaluating all neighbours in parallel.

Objective What the tuner is trying to optimise. run_obj: runtime minimises the mean (or median) solver runtime across instances; run_obj: quality minimises the mean (or median) numeric cost returned by the solver. See also: overall objective.

Overall objective (overall_obj) How per-instance results are aggregated into a single scalar for comparison. mean is sensitive to all instances including outliers; median is more robust but ignores magnitude differences. Note that adaptive capping always tests a running sum, so a median run prunes on a statistic it does not score — prefer pruning: false there.

Parameter space The set of all configurations defined by the .params file: parameter names, discrete domains, defaults, conditional activations, and forbidden combinations. RamParILS searches this space to find a good configuration.

Perturbation A random walk of perturbation_strength steps applied to the current local optimum to escape it and seed the next local search. Each step randomly changes one parameter to a uniformly sampled value from its domain. Larger values jump further in the space.

Pruning (see also: adaptive capping, capped score) Shorthand for adaptive capping: early termination once a candidate has spent its configured budget. Enabled by default (pruning: true).

Run objective (run_obj) What a single solver invocation measures: runtime (wall-clock seconds) or quality (a scalar cost returned by the solver). Both objectives are minimised.

Solver wrapper A script or executable that invokes the target algorithm with a given instance and parameter setting, then prints a result line in RamParILS format. See Solver protocol for the exact interface.

Strategy Synonym for configuration, commonly used in the context of automated reasoning solver portfolios (e.g., Grackle). A strategy is a complete parameter setting that defines the solver’s behaviour.

Strategy hash A compact fingerprint (64-bit integer) of the active configuration used as part of the cache key. It is computed from the sorted active param=value pairs, so inactive conditional values do not create duplicate cache entries. The hash is not guaranteed to remain portable across Rust versions.

Tuner timeout (tuner_timeout) The total wall-clock budget for the RamParILS run in seconds. Once elapsed, no new evaluations are started and the incumbent is returned. Distinct from cutoff_time, which limits individual solver runs.