We are solving a relatively large timetabling problem (15,000 decision variables) and we are trying to switch from IBM's CPLEX to a free solver. I am testing both CBC and Professor Nemhauser's MINTO solvers on NEOS website and I am using AMPL to make the models and the data files.

After solving my model I'd like to print out my results but "display x;" brings all zero while I know that there should be some ones in the solution (b/c the objective value is not zero and also I have checked the model on CPLEX and it is not infeasible)

Also none of the AMPL post processing commands work; for example the following for-loop command does not work

for {i in PAIR, j in ROOM, t in TIME: x[i,j,t]>0} print i," ", j," ", t, " ",x[i,j,t];

My hunch is that the AMPL implementation in COIN is not a standard implementation but I might be wrong. Do you know what I am doing wrong?

Thanks

asked 14 Mar '10, 22:11

Mark's gravatar image

Mark ♦
3.6k22350
accept rate: 9%


You might want to try using GLPK which uses an AMPL-like interface known as GMPL. This may prove easier for you.

http://www.gnu.org/software/glpk/

If you really want to use COIN than I recommend the MIP solver SYMPHONY. It can read AMPL files. From an FAQ...

What modeling languages and file formats does SYMPHONY work with?

SYMPHONY will read AMPL/GMPL files using GLPKs parser, or MPS file using COIN-OR's parser. It can also use FlopC++ as a modeling interface. 

http://www.coin-or.org/SYMPHONY/index.htm

link

answered 15 Mar '10, 12:58

larrydag%201's gravatar image

larrydag 1 ♦
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accept rate: 9%

Thanks I will give it a try. I was using COIN because I just wanted to quickly test a number of different solvers and that website provided many of them. Thanks again

(16 Mar '10, 02:10) Mark ♦

If you haven't done so already, you might want to ask on the Cbc mailing list.

link

answered 17 Mar '10, 21:01

Paul%20Rubin's gravatar image

Paul Rubin ♦♦
14.6k412
accept rate: 19%

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Asked: 14 Mar '10, 22:11

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