4.2.7.1. On Restart

These annotations and functions provide the basic building blocks to implement meta-heuristics triggered on restart and governed search with the use of solver internal values and functionality.

In this section: STATUS, basic_lns, complete, last_val, round_robin, sol, uniform_on_restart, on_restart.

Constants

STATUS

set of int: STATUS

Reports the status of the solver (before restarting).

Functions and Predicates

basic_lns

predicate basic_lns(var bool: nbh)

‘basic_lns’ provides LNS in its simplest form where one nbh is applied on every restart.

complete

test complete()

When complete is set to ‘true’, then it marks the search as complete.

last_val

predicate last_val(var bool: x)
function var float: last_val(var float: x)
function var $$E: last_val(var $$E: x)
function var opt $$E: last_val(var opt $$E: x)
function var set of $$E: last_val(var set of $$E: x)

Provides access to last values taken by a model variables. The last_val functions are only safe to use when the STATUS has been SAT or OPT.

round_robin

predicate round_robin(array [int] of var bool: nbhs)

round_robin provides a metaheuristic for LNS where each neighbourhood is chosen sequentially.

sol

predicate sol(var bool: x)
function var float: sol(var float: x)
function var $$E: sol(var $$E: x)
function var opt $$E: sol(var opt $$E: x)
function var set of $$E: sol(var set of $$E: x)
function array [$$E] of var bool: sol(array [$$E] of var bool: x)
function array [$$E] of var float: sol(array [$$E] of var float: x)
function array [$$E] of var $$F: sol(array [$$E] of var $$F: x)

Provides access to solution values of model variables. The sol function are only safe to use when the STATUS has been SAT or OPT.

uniform_on_restart

1.  function var $$E: uniform_on_restart($$E: low, $$E: high)

2.  function var $$E: uniform_on_restart(set of $$E: S)

3.  function var float: uniform_on_restart(float: low, float: high)

  1. Returns a new random value between low and high chosen from a uniform distribution whenver the solver restarts.

  2. Returns a new random value from the set S chosen from a uniform distribution whenver the solver restarts.

  3. Returns a new random value between low and high chosen from a uniform distribution whenver the solver restarts.

Annotations

on_restart

annotation on_restart(string: pred)

A search annotation that triggers a function to be executed on restart