From: Kish Shen <kisshen_at_cisco.com>

Date: Wed, 04 Aug 2010 14:43:09 +0100

Date: Wed, 04 Aug 2010 14:43:09 +0100

Stephan Schiffel wrote: > Hi all, > > Consider the following two examples: > > ?- minimize((member(X,[3,2,1]), Y=X), X). > Found a solution with cost 3 > Found a solution with cost 2 > Found a solution with cost 1 > Found no solution with cost -1.0Inf .. 0 > > X = 1 > Y = 1 > Yes (0.00s cpu) > > %%%%%% > > ?- hash_create(H), minimize((member(X,[3,2,1]), hash_add(H,solution,X)), X). > Found a solution with cost 3 > Found a solution with cost 2 > Found a solution with cost 1 > Found no solution with cost -1.0Inf .. 0 > > H = hash(4, 0, []) > X = 1 > > %%%%%% > > Why is Y in the first goal instantiated to 1 while the hash map in the second > goal does not contain the solution? Is there a way to make the second goal > work? > Hi Stephan, I assume you are using minimize/2 of the branch_and_bound library, and also lib(hash) for the hash tables. minimize works by remembering the best solution (non-logcially, so it survives backreacking), and when search is finished, the solution is unified with your problem variables, and you end up with the best solution. With minimize, the problem variables are those variables that are uninstantiated (i.e. still variables) when you start the search. This is the same state that branch-and-bound will be in when the search finished, i.e. the same variables should be variables, so the solution can be simply unified with the variables. Your hash table (H) is not a variable, so it will not be remembered. In more advanced versions of the branch_and_bound search (bb_min/6), you can specify a template for what you want to remember, but the hash table (and any other non-logical constructs, like handles) should not be included in the template, because they are unlikely to unify when you retrieve the best solution and unify it with the template. Cheers, Kish -- This e-mail may contain confidential and privileged material for the sole use of the intended recipient. Any review, use, distribution or disclosure by others is strictly prohibited. If you are not the intended recipient (or authorized to receive for the recipient), please contact the sender by reply e-mail and delete all copies of this message. Cisco Systems Limited (Company Number: 02558939), is registered in England and Wales with its registered office at 1 Callaghan Square, Cardiff, South Glamorgan CF10 5BT.Received on Wed Aug 04 2010 - 13:43:17 CEST

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