From: Kim Lai <kim73327_at_gmail.com>

Date: Fri, 25 Apr 2008 06:52:36 +0800

Date: Fri, 25 Apr 2008 06:52:36 +0800

hi, your reply is a great help for me. thanks.I use lib(eplex) to reformulate my problem as follow. and it really got a solution. But after I port the following code to C++. I'm getting trouble with ""How to extract the variables result"". A result like this "A2{0.0 .. 1.7976931348623157e+308 @ 1.1999999992549422}" I'd like to extract A2=1.199 = 1.2 But it's not even a string... in C++: I usually use "EC_word(Vars[i]).is_double(&d) == EC_succeed" to get a double or long int .....And this didn't work.. ------------eclipse code------------------------ - lib(eplex). solve(Vars, Cost) :- model(Vars, Obj), eplex_solver_setup(min(Obj)), eplex_solve(Cost), printf("%f %f %f", Vars ). model(Vars, Obj) :- Vars = [A1, A2, A3 ], Vars $:: 0..inf, M = 10000000, B1 :: 0..1, B2 :: 0..1, Obj $>= A1 + 1.2, Obj $>= A2 + 2.3, Obj $>= A3 + 1.3, A2 - A1 + B1*M $=< -0.2 + M, A2 - A1 + (1-B1)*M $>= 1.2 + M, A3 - A2 + B2*M $=< -0.4 + M, A3 - A2 + (1-B2)*M $>= 1.5 + M. -------------------------------------------------------------------------- thanks for ur reply :) On Thu, Apr 24, 2008 at 12:52 AM, Kish Shen <kisshen_at_cisco.com> wrote: > Hi Kim, > > Kim Lai wrote: > >> >> >> ---------- Forwarded message ---------- >> From: *Kim Lai* <kim73327_at_gmail.com <mailto:kim73327_at_gmail.com>> >> Date: Apr 23, 2008 10:56 PM >> Subject: Q: Linear Programming with Disjunction constraints >> To: eclipse-clp-users_at_lists.sf.net <mailto:eclipse-clp-users_at_lists.sf.net >> > >> >> hi, I'm new to eclipse. Here looks for a great HELP. >> after studying the documents... I still have trouble with my problem. >> I don't know how to use lib(eplex) for 1. disjunctive constraints >> 2. get a maximum among lots Varables >> >> The ECLiPSe documentation on eplex is not really designed to teach you > linear programming, or even constraint programming You would need to read > other source material (e.g. textbooks on linear programming and constraint > programming) for this. > > However, the issue of disjunctive constraint (which are non-linear, and > therefore cannot be directly modelled in linear programming) is discussed in > the ECLiPSe tutorial, in the chapter `Building Hybrid Algorithms' (section > 'Handling Disjunctions'). > > A well known aproach in linear programming to model disjunctions is to use > `Big-M constraints' -- this is discussed in the tutorial chapter. > > For your point 2, see below. > > I'd like to formulate a problem like this: >> >> ------------------------------------------------------------------------------ >> Vars = [ t1, t2, t3 ] >> Vars :: 0.0..inf >> >> % constraints >> (t1 - t2 <= -10.2 or t1 - t2 >= 15.6) and >> (t2 - t3 <= -3.1 or t2 - t3 >= 9.8 ) >> % goal ( cost ) >> try to minimize( Maximum among( t1 + 14.5, t2+1.4, t3+ 4.5 ) ) >> ------------------------------------------------------------------------- >> > > Looking at your example, you seem to be trying to model some sort of job > scheduling problem. The standard technique to model the minimum time to > complete a schedule is to add a `dummy' task that can only start after all > the other tasks have completed, and minimise the start time of this task as > your objective. > > If you are to model this in ic, you probably want to use finite domain > rather than real intervals -- to do this you need to have integers only, so > you need to choose your time unit so that they are integer, for your > example, this would seem to be in units of 0.1 seconds rather than seconds. > > This sort of problem can also be modelled as a linear problem using Big-M > constraints. > > The example page of the ECLiPSe website has several scheduling examples > (under the Planning and Scheduling section) which you might find useful to > look at: > > http://www.eclipse-clp.org/examples/index.html > > I will take a look at your specific code to see why you are getting the > error you are getting, but you should not need to use maxlist/2 with the > dummy task approach. > > Cheers, > > Kish > > -- ....Best Regards by Kim Lai, 賴廣甫 Welcome to visit http://kimklai.blogspot.comReceived on Thu Apr 24 2008 - 15:52:38 CEST

*
This archive was generated by hypermail 2.2.0
: Thu Feb 02 2012 - 02:31:58 CET
*