[eclipse-clp-users] More than one optimal solution using eplex.

From: Paul Cannongeyser <paul_dice_2_at_...75...>
Date: Wed, 30 Oct 2013 14:27:16 -0700 (PDT)
I ran this example from the tutorial and got a different but equally optimal solution.

----- eplex_10.ecl
% Transportation Problem Example.
% From http://eclipseclp.org/doc/tutorial/tutorial118.html#toc117
% entitled 16.3.3  Getting more solution information from the solver

% Run in this way: main2(Cost, Vars).
/*
?- main2(Cost, Vars).
Cost = 710.0
Vars = [16.0, 5.0, 0.0, 0.0, 25.0, 15.0, 34.0, 0.0, 0.0, 0.0, 0.0, 10.0]
Yes (0.00s cpu)

The tutorial has this as a solution:

Cost = 710.0
Vars = [0.0, 21.0, 0.0, 16.0, 9.0, 15.0, 34.0, 0.0, 0.0, 0.0, 0.0, 10.0]

*/

:- lib(eplex).

:- eplex_instance(prob). % a. declare an eplex instance

main2(Cost, Vars) :-
% b. create the problem variables and set their range
Vars = [A1,A2,A3,B1,B2,B3,C1,C2,C3,D1,D2,D3],
prob: (Vars $:: 0.0..1.0Inf),
% c. post the constraints for the problem to the eplex instance
prob: (A1 + A2 + A3 $= 21),
prob: (B1 + B2 + B3 $= 40),
prob: (C1 + C2 + C3 $= 34),
prob: (D1 + D2 + D3 $= 10),
prob: (A1 + B1 + C1 + D1 $=< 50),
prob: (A2 + B2 + C2 + D2 $=< 30),
prob: (A3 + B3 + C3 + D3 $=< 40),
% d. set up the external solver with the objective function
prob: eplex_solver_setup(min(
10*A1 + 7*A2 + 200*A3 +
 8*B1 + 5*B2 + 10*B3 +
 5*C1 + 5*C2 + 8*C3 +
 9*D1 + 3*D2 + 7*D3)),
 
%------------------------------- End of Modelling code
prob: eplex_solve(Cost), % e. Solve problem using external solver
(foreach(V, Vars) do
% f. set the problem variables to their solution values
prob: eplex_var_get(V, typed_solution, V)
).
-----

This is a quote from the same section of the tutorial:

"Note that, in general, an MP problem can have many optimal solutions, i.e. different solutions which give the 
optimal value for the objective function."

The tutorial has one optimal solution.  My recent run got another.

How do I get the same optimal solution as the tutorial?
Received on Wed Oct 30 2013 - 21:27:29 CET

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