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Re: [Help-glpk] Problem : basis
From: |
Andrew Makhorin |
Subject: |
Re: [Help-glpk] Problem : basis |
Date: |
Thu, 7 Jun 2007 13:54:43 +0400 |
> I tested my example of column generation 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
> Why? Normally, the precedent solution is feasible
> I don't understand spx_simplex because I don't use. How do I repear
> the problem? when the lpx_simplex is different of LPX_E_OK
If before changing the problem instance the basis was optimal, you
do not need to repair it. Probably you changed the status of some
rows/columns, or deleted some active rows and/or basic columns; this
invalidates the basis. If you need to delete an active row, just make
it free; similarly, to delete a basic column it is sufficient to fix
it at zero.