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Re: [Help-glpk] Save solution in GLPK
From: |
Cedric[FR] |
Subject: |
Re: [Help-glpk] Save solution in GLPK |
Date: |
Tue, 5 Jun 2007 17:51:01 +0400 |
I don't understand the zero bound.
My new column has a lower bound equal at zero.
So, It's always feasible.
And, the status is non-basis.
I tested my example without the routine lpx_std_basis
Now, the result is good:
0: objval = 0.000000000e+00 infeas = 1.000000000e+00 (0)
15: objval = 3.497400000e+04 infeas = 0.000000000e+00 (0)
* 15: objval = 3.497400000e+04 infeas = 0.000000000e+00 (0)
* 29: objval = 2.652371454e+02 infeas = 0.000000000e+00 (0)
OPTIMAL SOLUTION FOUND
* 29: objval = 2.652371454e+02 infeas = 0.000000000e+00 (0)
* 31: objval = 6.586143114e+01 infeas = 0.000000000e+00 (0)
OPTIMAL SOLUTION FOUND
But, At the 55 st problem, I obtain:
spx_simplex: initial basis is invalid
Andrew Makhorin wrote:
>
>>> At the second simplex, GLPK starts with an objval=0 instead of the
>>> precedent solution.
>>
>>> Why?
>>
>> If you add columns to the problem object, they become non-basic,
>> so the optimal basis must remain at least primal feasible, however,
>> it is primal infeasible (as seen from the solver output). Which
>> changes in the problem object did you make before re-optimiziation?
>> Looks like you changed bounds of some basic rows/columns.
>
> Make sure that after addition of new columns to the problem object
> they are non-basic and on their *zero* bounds. If a new column has
> a non-zero bound, adding it (along with the column of the constraint
> matrix) may make the basis primal infeasible.
>
>
>
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