[Cbc] Constraint to make a solution infeasible

[Terry]

Thanks for the tip Ed. That sounds like exactly what I want.

I changed repeat.cpp to use readLp instead of readMps. Then I was able to run it on my file.

Any idea why it only gives 3 answers, [2 0 0 2], [0 2 0 2], [1 1 1 1]? Then it gives up with:

Cbc0006I The LP relaxation is infeasible or too expensive
/coin/Coin-Pkg/bin/terry/ex2.lp took 0.00074 seconds, 0 nodes with objective 1.79769e+308 Finished


I added bounds 0 to 10 for each variable and I tried changing the obj and constraints slightly, but I could not get it to give more than 2 or 3 solutions before failing. I guess there's a lot more I need to understand first.

Terry



On Jun 12, 2011, at 7:56 PM, Ed Bulog wrote:

> Hi Terry,
> 
> While I'm far from an expert, I remember that the "repeat.cpp" example (https://projects.coin-or.org/Cbc/browser/stable/2.7/Cbc/examples/repeat.cpp) essentially does this. I believe it repeatedly finds the optimal solution and then adds a cut to remove it, so that you end up with the 20 "best" solutions. Hope that helps you.
> 
> Cheers,
> 
> Ed
> 
> On 13 June 2011 11:08, Terry <maillst at aol.com> wrote:
> 
> CBC will find an optimal solution to my IP problem. Now I want the "next" optimal solution. That is, I want to make the previous solution infeasible and run CBC again to find another solution.
> 
> Here's an example I'm working with:
> 
> Minimize
>  x1 + x2 + x3 + x4
> Subject To
>  5 x1 +  5 x2 >= 10
>  7 x3 + 14 x4 >= 21
> Integers
>  x1
>  x2
>  x3
>  x4
> End
> 
> 
> Optimal - objective value 4.00000000
>      0 x1                     2                      1
>      1 x2                     0                      1
>      2 x3                     1                      1
>      3 x4                     1                      1
> 
> 
> Can I add a constraint so that [2 0 1 1] is infeasible, but allows any other answer? I'm afraid this is a stupid question, but I don't see how to do it.
> 
> Thanks.
> Terry
> 
> 
> 
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