A.55.4.1 Example 1

This is the "radiation therapy" example, taken from Introduction to Operations Research by Hillier and Lieberman.

Prolog DCG notation is used to implicitly thread the state through posting the constraints:

:- use_module(library(simplex)).

radiation(S) :-
        gen_state(S0),
        post_constraints(S0, S1),
        minimize([0.4*x1, 0.5*x2], S1, S).

post_constraints -->
        constraint([0.3*x1, 0.1*x2] =< 2.7),
        constraint([0.5*x1, 0.5*x2] = 6),
        constraint([0.6*x1, 0.4*x2] >= 6),
        constraint([x1] >= 0),
        constraint([x2] >= 0).

An example query:

?- radiation(S), variable_value(S, x1, Val1),
                 variable_value(S, x2, Val2).
Val1 = 15 rdiv 2,
Val2 = 9 rdiv 2.