Optimization constraints
Author: Daniel Diaz
Keywords: GNU Prolog, manual, Prolog, compiler, constraints, finite domains

### 9.10 Optimization constraints

- fd_minimize/2, fd_maximize/2

#### 9.10.1 fd_minimize/2, fd_maximize/2

Templates

  fd_minimize(+callable_term, ?fd_variable)
  fd_maximize(+callable_term, ?fd_variable)

Description

fd_minimize(Goal, X) repeatedly calls Goal to find a value that minimizes the variable X. Goal is a Prolog goal that should instantiate X, a common case being the use of fd_labeling/2 (section 9.9.1). This predicate uses a branch-and-bound algorithm with restart: each time call(Goal) succeeds the computation restarts with a new constraint X #< V where V is the value of X at the end of the last call of Goal. When a failure occurs (either because there are no remaining choice-points for Goal or because the added constraint is inconsistent with the rest of the store) the last solution is recomputed since it is optimal.

fd_maximize(Goal, X) is similar to fd_minimize/2 but X is maximized.

Errors

Goal is a variable |  | instantiation_error
Goal is neither a variable nor a callable term |  | type_error(callable, Goal)
The predicate indicator Pred of Goal does not correspond to an existing procedure and the value of the unknown Prolog flag is error (section 8.22.1) |  | existence_error(procedure, Pred)
X is neither a variable nor an FD variable nor an integer |  | type_error(fd_variable, X)

Portability

GNU Prolog predicates.

Copyright (C) 1999-2021 Daniel Diaz Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved. More about the copyright