Re: [Help-glpk] Problem : basis

[Cedric[FR]]

Yes, I delete Rows and Cols

For Row, must I use glp_set_row_stat(lp , i , GLP_NL)?

For Column, must I use glp_set_col_stat(lp , i , GLP_NL)?

How can I fix my column at 0?

must I resolve my problem before to add column or row?

Or

must I only start again the routine lpx_std_basis(lp)?


Andrew Makhorin wrote:
> 
>> 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.
> 
> 
> 
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