help-glpk
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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.





reply via email to

[Prev in Thread] Current Thread [Next in Thread]